Series 12 passenger cars were express seat passenger cars that were manufactured between 1969 and 1978, and that support a maximum speed of 110km / h. It was equipped with a diesel-generator-powered air conditioner under the floor, which was not inferior to that of trains and trains at that time, and became the basis for the new passenger cars of the 14th series and later. Initially it was also operated as a temporary train and Osaka Expo transport, and later as a regular express train, and was active in various parts of the country except Hokkaido. In later years, various applications such as remodeling to the commuting type and remodeling to the joyful train can be seen, and you can see that they are still active as passenger cars for waves.