­^¤åºK­n I/O, resource-based theory ,or strategic group are usually used for analyzing the competition in industries in the past., but they seldom show the tiny reciprocal interaction between companies. So this research use case study to demonstrate the rivalry between companies in an industry. This research take TV-game machine companies as research targets. The scope starts from Nintendo entering this industry in 1983 to SEGA leaving this industry in 2001. Because the relative researches for TV-game machine were quite few, therefore this research starts from the information gathering about this industry, that trying to mention the outline and nature of TV-game machine industry. Then analyze this industry by rivalry theory. At last, according to the theories and the real competition between companies, this research infers the propositions and findings. The findings are: The TV-game machine industry is greatly influenced by three components; they are the TV-game machine companies, software companies, and consumers. Thanks to that the software companies have to give money to the TV-game machine companies, so TV-game machine companies profit from not only the consumers, but also the software companies. And the willing for consumers to buy a TV-game machine is affected by the function of the machine itself and the amount of games issued by the software companies. From the history of the TV-game machine, this research finds the issue of TV-game machines has the phenomenon of discontinuous invention. From 8 digital, 16 digital, 32 digital, 64 digital, to 128 digital, companies penetrate market by issuing more powerful TV-game machines. Though this discontinuous invention has the effect to raise the rank of companies, but due to the difference of specification between the new type and the old one, the new generation is not able to play the software for the old one. The environmental factors faced by the TV-game machine companies are: 1.The difference of machines between each company is not specific; 2.The entry barrier for TV-game machine industry is high; 3.The amount of sells is affected by time and software; 4.The market uncertainty often rises for the sake of low supply; 5.The market commonality is high. This research has the following findings: 1.To compare with common condition, when the life of products goes into the decline period, the monopolizing companies may take price competition as the means to increase the selling of products. 2.In monopolizing industry, companies seldom attack. But if some company takes tactic attack action, other companies will response quickly. 3.The companies will think over the reputation of other competitors in the industry before attacking, if the competitors had the records of responding strongly after being attacked, the companies may not attack; 4.In fast-cycled industry, if the companies issue new products in a hurry, the advantage of first mover is not obvious; 5.When companies don¡¦t have enough resource to take strategic action, they may take tactic action as substitute; 6.In fast-cycled industry, when companies involved in have immense scale, they can ask their suppliers to produce specific products just for them via their strong negotiation power; 7.To the contrast of initial period of industry, the entry barrier is higher in the mature period. When industry gets mature gradually, the firms have to issue specific products which have not only good quality to satisfy spoiled consumers. When industry gets into mature period, firms will take action to raise their market share.