A mode changeover control system for a transmission wherein the starting of a vehicle can be prevented even if the transmission is changed over to the drive mode side while a side stand is in an erected position. In a motorcycle including a mode changeover mechanism for a continuously variable transmission, and a side stand, there is provided a changeover operation section changed over by the driver between operation positions corresponding respectively to a drive mode position and a neutral mode position of the mode changeover mechanism. An electronic control unit operates the mode changeover mechanism based on the changeover operation position of the changeover operation section. The control section is configured so as to continually maintain the mode changeover mechanism in the neutral mode position even if the changeover operation section is operated to a drive mode operation position while the side stand is in a stored position.