A speed change device for a traveling vehicle comprising: a thrust shaft connected to an engine; a speed change mechanism for changing between a high and a low speed provided to the thrust shaft; a counter shaft for transmitting an output from the speed change mechanism for changing between a high and a low speed; a mechanism for switching between advancing and retracting provided to the counter shaft, the mechanism having a forward-rotation idler gear rotatably supported on the thrust shaft; a speed change shaft for transmitting reverse-rotation power from the counter shaft as forward-rotation power via the forward-rotation idler gear; a driven shaft provided as an extension to the thrust shaft; and a main speed-change mechanism having a driving gear group provided to the speed change shaft and a driven gear group provided to the driven shaft.