PURPOSE: To suppress increasing of weight of a chain cover, effectively improve its rigidity, and prevent occurrence of film oscillation by forming a reinforcing rib which is projected to an inner space of a chain chamber along an outer periphery of a cam sproket of a chain cover.

CONSTITUTION: A chain cover forms a chain chamber for circulation of a chain on a front side of an engine block of a V-type engine. In such a structure, a connection flange 35 in respect to a rear chain cover 5 is formed on a peripheral edge of a front chain cover 6 provided so as to cover a front side of the rear chain cover 5. In this case, a reinforcing rib 36 is provided on the front chain cover 6, which rib 36 is bent along an outer periphery of a first intake cam sproket, and projected to the inner space of the chain chamber. An expansion part 39 is formed on the front chain cover 6, which expansion part 39 has a portion opposite to the first cam sproket and expanded to the outer side of the chain chamber. It is thus possible to improve rigidity of the chain cover and prevent occurrence of film oscillation.