This article examined the market structure of Japanese automobile industry during the high-speed economic growth period. According to the rapid economic growth from !955 until 1974, the number of vehicle registration has highly increased. Some characteristics of Japanese automobile market structure were formed during that period. One of the characteristics is the high ratio of truck number, which was originated from the three-wheel trucks that were mostly used until the beginning of 1960s in Japan. And, mini four-wheel trucks that are popularly used for transportation of small quantity and short distance, were developed by the three-wheeler manufactures. Concerning car sector, mini-car and popular-car which were below 1000cc of engine displacement, played important role in the process of motorization. The ratio of both cars was like that of western European countries. Small scale businessmen preferred popular car to mini-car that was below 360cc of engine displacement. On the contrary, paid workers preferred mini-car to popular-car. The cause of such characteristics of car sector and truck sector was the strategic response of automobile manufactures. And, by the response to the such market structure, Japanese automobile manufacturers strengthened the international competitiveness.