To provide a gear train for an engine reducing unit cost without reducing a lifetime.

The gear train for the engine is provided with a crank gear 21 provided on a crankshaft 13 of the engine 10, a cam gear 22 provided on a camshaft 14 of a cylinder head 12, and one or more intermediate gears 23, 24 transmitting rotation of the crank gear 21 to the cam gear 22. The crank gear 21, the one or more intermediate gears 23, 24, and the cam gear 22 are forged gears made of steel material provided by forging carbon steel or cast gears made of cast iron provided by casting cast iron. The crank gear 21, the one or more intermediate gears 23, 24, and the cam gear 22 are selected from the cast gears and the forged gears in such a manner that the forged gears and the cast gears are alternately arranged and mutually mesh.