A transmission system for a vehicle has a shift driving mechanism which operates, under control by a control unit, at the time of shifting the gear position, to disengage a transmission gear of a current gear position and a shifter from each other after engaging a transmission gear of a next gear position and a shifter with each other in a condition where a transmission clutch that transmits power to the transmission gear of the next gear position is in an engaged state. This ensures smoother and swifter shifting of gear position.