Abstract: Provided is a track car drive system, which is assisted by a generator motor so that it may attain a gear array for equalizing the number of speed range and the gear ratios at the individual gears as a transmission for the forward speed and the backward speed and which can be combined with the generator motor. A transmission (15) for receiving the output of an engine (14) at an input shaft (30) is constituted by combining a forward range (31) and a backward range (32) with two intermediate shafts (41 and 42) having different speed ranges (51 to 54) between themselves and an output shaft (45). By shifting/fastening a first clutch (43) or a second clutch (44) selectively, the rotation of either the forward range (31) or the backward range (32) is transmitted to either of the intermediate shafts (41 and 42). When one of the speed ranges (51 to 54) is selected, the same gear number and gear ratio are taken no matter whether the track car might run forward or backward.