A control part controls a clutch actuator. The control part has a first shift mode and a second shift mode. In the first shift mode, the clutch is switched to the disengaged state before changing of the gear position and the clutch is switched to the engaged state after changing of the gear position. In the second shift mode, an output of the prime mover is adjusted while the clutch is kept in the engaged state during the shift operation. Either the first shift mode or the second shift mode is selected on the basis of a detection result on whether the shift operation is a shift-up operation or a shift-down operation, and a traveling state of the vehicle.