To provide an engine that improves versatility and durability of components and reduces costs for improving fuel economy, while reducing weight.

The engine includes a piston 1 provided slidably in a cylinder and a connecting rod 2 connecting the piston 1 to a crankshaft. Further, the engine includes a shaft member 3 which has a first shaft part 4 supported on the side of the piston 1, and a second shaft part 5 supported on the side of the connecting rod 2, to connect the piston 1 and the connecting rod 2 to each other. The engine includes an elastic member 6 which is interposed between the first shaft part 4 and second shaft part 5, and displaces the first shaft part 4 from the second shaft part 5 in a sliding direction of the piston 1 according to pressure that acts on the piston 1.