Engine that includes blow-by-gas returning system

An engine that includes a blow-by-gas returning system, the engine being configured to direct blow-by gas within a crankcase to an intake system through an inside of a head cover,

• wherein the intake system includes a cover intake-passage disposed at the head cover, and the cover intake-passage communicates with a blow-by-gas passage of the head cover,
• the cover intake-passage forms part of a suction passage that connects an air cleaner with a supercharger, and the cover intake-passage is integral with the head cover,
• a bottom wall of the blow-by-gas passage includes a return hole through which oil collected within the blow-by-gas passage drops,
• the bottom wall includes a descending slope that is around the return hole and becomes lower toward the return hole, and
• the blow-by-gas passage communicates with the cover intake-passage through a communication hole of a gasket, the gasket being held between the blow-by-gas passage and the cover intake-passage.