When temperature of lubricating oil is raised at a time of low-temperature, of an outer peripheral side of a radial plain bearing in a bearing retaining unit, heat is not supplied from a heating medium in a thermal medium flow path on the outer peripheral side of a halved bearing metal in a bearing retaining unit body, which has a large thermal capacity, and instead, heat is supplied from the heating medium in the thermal medium flow path on the outer peripheral side of a halved bearing metal in the cap, which has a small thermal capacity.