Abstract: A gas valve driving apparatus of a gas engine in which a gas supply passage is connected to an intake means of the engine, comprises a gas valve arranged in the gas supply passage; a gas valve cam provided on a cam shaft in a cam chamber formed by a cylinder block of the engine and being independent of an intake cam and an exhaust cam on the cam shaft; and connecting means operable to connect the gas valve cam and the gas valve together, so that the gas valve cam may drive the gas valve through the connecting means. The connecting means may be provided with a rocker arm or may be provided with a tappet. The tappet and the gas valve are aligned on a same line extending toward the center of the cam shaft.