A clutch actuator mounting structure for internal combustion engine has excellent maintainability such that clutch actuator maintenance and the like can be carried out without dismounting an engine case. The clutch actuator mounting structure for an internal combustion engine includes, in the engine case, a power transmission mechanism designed to transmit rotational power of a crankshaft to an output shaft through a shift clutch and a transmission. The engine case is formed with a clutch actuator containing part in which a clutch actuator for engaging/disengaging the shift clutch is contained. The clutch actuator containing part has a clutch actuator mounting/dismounting port through which to mount and dismount the clutch actuator. The clutch actuator mounting/dismounting port is formed to be exposed to the exterior.