PURPOSE: To suppress resonance noise generated by vibration of a timing belt in a V-shaped belt passage part formed of a timing belt cover.

CONSTITUTION: A protrusion part 20 approximating to an internal combustion engine main unit front surface is provided so that right/left belt passage parts are spaced, in a central part reverse surface of a timing belt cover lower part 13 for constituting a lower part of a timing belt cover. The protrusion part 20 is provided without relationship to a seal position of a side edge of the timing belt cover lower 13 and previously press-molded in a shape corresponding to an irregular shape of the engine main unit front surface.