A vehicle power transmission system comprising: a transmission for transmitting a driving force of an engine mounted in a vehicle to a drive wheel of the vehicle while changing a rotational speed; a clutch for transmitting or shutting off the driving force transmitted from the engine to or from the transmission, the clutch including a clutch hub, a clutch plate, a friction plate, a pressure plate and a pressure elastic body, the clutch hub for holding the clutch plate placed facing the friction plate to be rotationally driven by the driving force transmitted from the engine and for transmitting the driving force to the transmission; the pressure plate placed adjacently to the clutch hub so as to be approachable to and separable from and relatively rotatable with respect to the clutch hub, the pressure plate elastically pressing the friction plate or the clutch plate by the pressure elastic body; the clutch hub comprising a hub-side assist cam portion and a pressure-side assist cam portion, the hub-side assist cam portion and the pressure-side assist cam portion being included in the clutch hub and the pressure plate of the clutch respectively, the hub-side assist cam portion and the pressure-side assist cam portion each including an inclined surface and being adapted to generate an assist force increasing a pressing force between the friction plate and the clutch plate upon generation of a relative rotation between the clutch hub and the pressure plate when the clutch shifts to a state where the driving force is transmitted; a clutch actuator including an electric motor for applying, to the pressure plate, a clutch OFF pressing force and an anti-assist force, the clutch OFF pressing force separating the pressure plate from the friction plate or the clutch plate against an elastic force of the pressure elastic body in order to put the clutch in a state where the driving force is shut off; characterized in that the vehicle power transmission system further comprises a control device comprising a microcomputer for automatically controlling operation of the clutch actuator and automatically controlling the transmission and shutting off of the driving force in the clutch, the control device, when the clutch is caused to shift to the state where the driving force is transmitted, automatically controlling the operation of the clutch actuator to make the clutch OFF pressing force to be applied to the pressure plate less than the elastic force of the pressure elastic body and apply, to the pressure plate, the anti-assist force being less than the assist force against the assist force, in order to suppress the increase of the assist force. a transmission for transmitting a driving force of an engine mounted in a vehicle to a drive wheel of the vehicle while changing a rotational speed; a clutch for transmitting or shutting off the driving force transmitted from the engine to or from the transmission, the clutch including a clutch hub, a clutch plate, a friction plate, a pressure plate and a pressure elastic body, the clutch hub for holding the clutch plate placed facing the friction plate to be rotationally driven by the driving force transmitted from the engine and for transmitting the driving force to the transmission; the pressure plate placed adjacently to the clutch hub so as to be approachable to and separable from and relatively rotatable with respect to the clutch hub, the pressure plate elastically pressing the friction plate or the clutch plate by the pressure elastic body; the clutch hub comprising a hub-side assist cam portion and a pressure-side assist cam portion, the hub-side assist cam portion and the pressure-side assist cam portion being included in the clutch hub and the pressure plate of the clutch respectively, the hub-side assist cam portion and the pressure-side assist cam portion each including an inclined surface and being adapted to generate an assist force increasing a pressing force between the friction plate and the clutch plate upon generation of a relative rotation between the clutch hub and the pressure plate when the clutch shifts to a state where the driving force is transmitted; a clutch actuator including an electric motor for applying, to the pressure plate, a clutch OFF pressing force and an anti-assist force, the clutch OFF pressing force separating the pressure plate from the friction plate or the clutch plate against an elastic force of the pressure elastic body in order to put the clutch in a state where the driving force is shut off; characterized in that the vehicle power transmission system further comprises a control device comprising a microcomputer for automatically controlling operation of the clutch actuator and automatically controlling the transmission and shutting off of the driving force in the clutch, the control device, when the clutch is caused to shift to the state where the driving force is transmitted, automatically controlling the operation of the clutch actuator to make the clutch OFF pressing force to be applied to the pressure plate less than the elastic force of the pressure elastic body and apply, to the pressure plate, the anti-assist force being less than the assist force against the assist force, in order to suppress the increase of the assist force.