An arrangement structure of a shifting actuator of an internal combustion engine mounted on a motorcycle is provided in which while the shifting actuator is provided externally of an engine case of the engine so as not to interfere with auxiliaries, it is protected without external protrusion and external appearance is kept satisfactory. An external wall of an engine case is partially inwardly recessed to form a recessed portion capable of accommodating a shifting actuator. An actuator body of the shifting actuator is disposed in the recessed portion. An attachment bracket attached to an end portion of the actuator body is fitted to a first fitting hole of an engine case outer lateral wall on the side of the recessed portion and is secured to the engine case outer wall. The motorcycle has a multistage transmission that can reduce its axial width to achieve compactness.