A crankshaft bearing part (11) has a pair of main bearing metals (41), and lubricating oil is guided from an oil gallery to an inner circumferential oil groove (43) through an in-block oil passage (33) and a first oil hole (42). Some of the lubricating oil is supplied to a control shaft bearing part (17) via a second oil hole (44) and an in-cap oil passage (34). Lubricating oil is guided from a third oil hole (46) in a pair of control shaft bearing metals (45) to an inner circumferential oil groove (47). The oil groove (43) in the crankshaft bearing part (11) functions also as an oil passage for supplying lubricating oil to the control shaft bearing part (17), thereby achieving a simple configuration.