A motorcycle has a transmission including a transmission mechanism and an electronic control unit (ECU). The transmission mechanism includes a crankshaft as an input shaft, a driven shaft as an output shaft and an electric motor. The electric motor changes continuously the transmission ratio between the crankshaft and the driven shaft. The ECU estimates the heat value of the motor from a rate of change in the transmission ratio. When the estimate heat value reaches or exceeds a specified value the electric motor is restricted or stopped.