Abstract: A transmission for a tractor has an input shaft receiving power from an engine, an idle shaft disposed parallel with the input shaft, an output shaft disposed parallel with the idle shaft and transmitting power to a main transmission part, forward/reverse driving gears installed on the input shaft so as to rotate idle, a forward/reverse clutch installed between the forward driving gear and the reverse driving gear to selectively connect the forward driving gear or the reverse driving gear to the input shaft, a forward driven gear installed on the idle shaft and engaged with the forward driving gear, a reverse driven gear installed on the idle shaft and engaged with the reverse driving gear, high speed/low speed driving gears installed between the forward driven gear and the reverse driven gear so as to rotate idle, a high speed/low speed clutch installed between the high speed driving gear and the low speed driving gear to selectively connect the high speed driving gear or the low speed driving gear to the id