First derrick car called SO-1 type was designed for bridge erection by Japanese Government Railways, and 6 units of them had been built from 1920 to 1927. This derrick car was capable of erecting up to 70ft span and 28ton weight class plate girder bridge. Though based on the past similer idea, the car was an original one for railway use, and it contributed very much to construction of railway network at that time. This erection method was characterized in that it made the bridge erection safer, faster and more economical than the former staging erection. But it retired about 1960', because a new bridge erection has been developed thereafter, and a new derrick car SO-200 type appeared in 1960. This paper discribes a history of the first derrick car for bridge erection.