Blowby gas control apparatus for internal combustion engine

In a four-stroke cycle internal combustion engine to be mounted to a vehicle having a start clutch, a blowby gas control apparatus for an internal combustion engine is provided which can reduce variations in number of engine revolution before connecting a clutch to improve the ride quality. It comprises: a new air introducing channel (131) for introducing new air into a crankcase (C); a blowby gas return channel (135) for returning blowby gas in the crankcase C to an air-intake system; a control valve (140) provided at least one of the new air introducing channel (131) and the blowby gas return channel (135) for opening and closing the channel; and control means (141) for opening and closing the control valve (140) under control, wherein the control means (141) switches the control valve (140) from the closed state to the opened state with the start clutch (91) connected when the vehicle starts traveling.