Operability of a shift lever is improved. To achieve this, a main speed change mechanism and an auxiliary speed change mechanism are arranged in a transmission case, and a main shift lever is interlockingly connected to a shift fork provided at the main speed change mechanism through an interlock shaft. On the other hand, an auxiliary shift lever is interlockingly connected to a shift fork provided at the auxiliary speed change mechanism, and the main shift lever is provided in the vicinity of the auxiliary shift lever through the interlock shaft. |