A track car drive system having an engine and a transmission for changing a speed of a rotation output of the engine and outputting the same, wherein the rotation of an output shaft of the transmission is transmitted to drive wheels of the track car, wherein: the transmission comprises a first intermediate shaft and a second intermediate shaft arranged in parallel with an input shaft, multiple sets of speed ranges (51, 52, 53, 54) disposed between and engaged with the first intermediate shaft or the second intermediate shaft and the output shaft for selectively transmitting power, and a forward range and a backward range disposed between the input shaft and the two intermediate shafts for selectively transmitting the rotation of the input shaft, wherein a number of gear shift steps obtained by the combination of the selection of the forward range or the backward range and the selection of the multiple sets of speed ranges is equal for forward movement and backward movement; the system further comprises a generator motor for outputting power from or inputting power to a battery via an inverter; the generator motor provides rotation power to or receives rotation power from the first intermediate shaft and/or the second intermediate shaft provided in the transmission; characterized in that: a differential mechanism is disposed between the generator motor and the first and second intermediate shafts, the differential mechanism having a connect gear train composed of a plurality of gears arranged in line between at least the first or the second intermediate shaft, and further having a fixing clutch for constraining the rotation of the gears of the connect gear train; and in that the generator motor is connected to a differential output shaft of the differential mechanism. the transmission comprises a first intermediate shaft and a second intermediate shaft arranged in parallel with an input shaft, multiple sets of speed ranges (51, 52, 53, 54) disposed between and engaged with the first intermediate shaft or the second intermediate shaft and the output shaft for selectively transmitting power, and a forward range and a backward range disposed between the input shaft and the two intermediate shafts for selectively transmitting the rotation of the input shaft, wherein a number of gear shift steps obtained by the combination of the selection of the forward range or the backward range and the selection of the multiple sets of speed ranges is equal for forward movement and backward movement; the system further comprises a generator motor for outputting power from or inputting power to a battery via an inverter; the generator motor provides rotation power to or receives rotation power from the first intermediate shaft and/or the second intermediate shaft provided in the transmission; characterized in that: a differential mechanism is disposed between the generator motor and the first and second intermediate shafts, the differential mechanism having a connect gear train composed of a plurality of gears arranged in line between at least the first or the second intermediate shaft, and further having a fixing clutch for constraining the rotation of the gears of the connect gear train; and in that the generator motor is connected to a differential output shaft of the differential mechanism. a differential mechanism is disposed between the generator motor and the first and second intermediate shafts, the differential mechanism having a connect gear train composed of a plurality of gears arranged in line between at least the first or the second intermediate shaft, and further having a fixing clutch for constraining the rotation of the gears of the connect gear train; and in that the generator motor is connected to a differential output shaft of the differential mechanism.