會計學教課書都教學生：決策之作成，應從成本效益出發，至於過去已投入的成本屬沉沒成本，非攸關，不應影響決策，讀者少有質疑，但事實究竟如何？實務上，決策者做決策時，考量之因素甚多，不會只有成本一項，不過教課書多只著重成本一項，這又與事實相左。本研究以「核四決策」為例，探討實務上決策之作成，在諸多因素中沉沒成本是否真的沒攸關性。 核四應否停建，不論在能源、社會政策等層面皆具高度爭議性。本研究結合會計領域與重大公共政策議題，藉支持/反對停建核四之觀點，辨認決策者或旁觀者所在乎之因素，如已投入興建成本、完工程度、預期尚需投入成本、經濟結果，以及核能安全、核電廠可能面臨的風險等，再探討決策者對停建核四的態度是否受沉沒成本或其他因素之影響；以及，決策者的知識背景（會計系、政治系）及政治理念是否影響決策者的上述認知。 本研究透過問卷搜集資料，發現已投入之核四興建成本（即沉沒成本）顯著影響受測者贊成停建與否的態度：當受測者越覺得沉沒成本重要，越傾向反對停建核四，有沉沒成本效果存在。本研究也發現受測者最重視的細項決策因素，為「臺灣若發生類似福島核災之核災損失」。對臺灣而言，日本福島本具時間、地理、文化上的相近性，再加上媒體敘事的渲染力，福島核災創造人民對於核災的公共想像及恐懼。在其他因素中，「非核家園」之理念亦顯著影響核四決策：當受測者越覺得「非核家園」之理念重要，越傾向贊成停建核四。本研究還發現受測者的知識背景影響其對沉沒成本的態度：評估核四決策時，政治系受測者較會計系受測者，易受沉沒成本影響，將沉沒成本視為攸關。再者，政治理念對於受測者贊成停建與否的影響，當受測者對候選人的偏好為江宜樺先生等人，其立場以反對核四停建居多；當受測者對候選人的偏好為蔡英文女士等人，其立場以贊成核四停建居多。 本研究發現臺電的溝通效果不佳，除數據之可靠性待加強外，傳遞的資訊並未針對問題的核心，例如核能安全很受受測者重視，然而臺電於說明核電廠之安全時，使用「複合式災害」來描述福島核災，複合來自地震及海嘯，而事實上福島核災係因海嘯而造成，海嘯因地震而引發；臺灣外海斷層之地理構造使臺灣核電廠區域縱有大地震時，也不會遭遇如福島般的大海嘯。 因此本研究建議臺電和行政機關，應針對核能安全及核能政策，辨認人民容易產生誤解的資訊為何，以正確的用詞精確澄清。此外，非會計背景之決策者，應加強關於沉沒成本的認知；會計背景之決策者，應抱持批判性思考的態度，質疑「沉沒成本不應該影響決策」的理論是否事實上成立。 / There is an undoubted rule always on accounting textbooks, which is, decision making should base on the cost-benefit analysis, as for the investment in the past belongs to sunk cost and is irrelevant to the decision making. However, is this legit? There are so many concerns beyond the cost when decision maker making decision, but most textbooks only focus on the cost, which is different from the turth. This research takes “the decision making in Lungmen nuclear power plant” as a case study, to examine whether sunk cost is truly irrelevant to decision making in reality. The issue that whether construction of Lungmen nuclear power plant should be suspended is highly controversial, no matter in aspect of energy, social policy and so on. First, across accounting and public issues, the researcher collects the viewpoints from pros and cons toward this issue, and identifies decision factors, for examples, the invested construction cost (which means sunk cost here), the degree of project completion, future expected cost, economic results, and nuclear safety, probable risk of nuclear power plant. Second, this research examines whether sunk cost or other factors influence decision makers’ attitude toward the issue. Third, whether knowledge backgrounds (major in accounting or political science) and political ideologies of decision makers influence their cognitions about sunk cost and the issue. By questionnaire survey, the results of this research found: First, sunk cost does influence receivers’ attitude toward the issue: the more important receivers think sunk cost is, the more they against the construction to be suspended; sunk cost effect has been observed. Second, among factors, receivers take Japan’s Fukushima nuclear disaster most serious. We argue that Fukushima nuclear disaster’s timing, geography and Japan’s culture are close to Taiwan, thus the disaster deepen public imagination and fear about the nuclear disaster. Third, the idea of nuclear-free homeland also influences decision making in the issue: the more important receivers think the idea is, the more they support the construction to be suspended. Forth, receivers’ knowledge backgrounds influence their cognitions about sunk cost: compared with receivers major in accounting, receivers major in political science take sunk cost as a relevant factor. Fifth, political ideologies of receivers influence their attitude toward the issue: when receivers vote to Jiang Yi-Huah etc., most of them against the construction to be suspended; when receivers vote to Tsai Ing-Wen etc., most of them support the construction to be suspended. Sixth, Taiwan Power Company doesn’t have effective communication with the public. Not only reliability of its data, but the covey of core information should be improved. For example, it describes Fukushima nuclear disaster as a “compound disaster” including earthquake and tsunami, but actually the disaster happened only due to tsunami caused by earthquake. The geological formation of offshore faults of Taiwan is different to Japan, thus there will be no Fukushima-like tsunami in Taiwan. This research suggest: First, Taiwan Power Company and executive administration should identify the information that public easily misunderstood, especially about nuclear safety and energy policy, and then clarify with proper words. Second, decision makers with non-accounting background should improve their knowledge about sunk cost. Third, decision makers with accounting background should have critical thinking about whether the theory that “sunk cost is irrelevant to decision-making” is found in reality.