A variable compression ratio mechanism of a reciprocating engine includes at least an upper link connected at one end to a piston pin and a lower link connecting the other end of the upper link to a crankpin. At top dead center, when hypothetical connecting points between the upper and lower links are able to be supposed on both sides of the line segment connecting the piston-pin center and the crankpin center, and the first one of the connecting points has a smaller inclination angle, measured in the same direction as a direction of rotation of the crankshaft, from the axial line of reciprocating motion of the piston-pin center and to a line segment connecting the piston-pin center and the first connecting point; as compared to the second connecting point, the first connecting point is selected as the actual connecting point.