A power unit device for a vehicle, comprising: an engine; a differential device that is arranged on one vehicle-width-direction side of an engine; a drive shaft (20, 30), wherein, from the differential device, the drive shaft (20, 30) is inserted into an oil pan of the engine and extends toward the other vehicle-width-direction side; a heat insulating member configured to cover an outer side of the oil pan; and a differential housing configured to house the differential device and configured to be fitted to and mounted on one vehicle-width-direction side of the oil pan, wherein a fitting portion that is formed in a cylindrical shape is provided in the differential housing, a fitted portion that is formed in a cylindrical shape and to which the fitting portion of the differential housing is fitted is provided in the oil pan, a fitting face portion (43a, 75a) of one of the fitting portion of the differential housing and the fitted portion of the oil pan is fitted to a fitting face portion (43a, 75a) of the other of the fitting portion of the differential housing and the fitted portion of the oil pan, the fitting face portion of the differential housing is formed by an outer peripheral face of the fitting portion of the differential housing, the fitting face portion of the oil pan is formed by an inner peripheral face of the fitted portion of the oil pan, and an outer diameter of the fitting face portion of the differential housing is formed so as to be smaller than an inner diameter of the fitting face portion of the oil pan, characterized in that the fitting face portion (43a, 75a) of the one of the fitting portion of the differential housing and the fitted portion of the oil pan comprises, at different positions in a circumferential direction, a plurality of recesses recessed in a radial direction and a plurality of projections protruding in the radial direction, and is fitted to the fitting face portion (43a, 75a) of the other of the fitting portion of the differential housing and the fitted portion of the oil pan by the plurality of projections. an engine; a differential device that is arranged on one vehicle-width-direction side of an engine; a drive shaft (20, 30), wherein, from the differential device, the drive shaft (20, 30) is inserted into an oil pan of the engine and extends toward the other vehicle-width-direction side; a heat insulating member configured to cover an outer side of the oil pan; and a differential housing configured to house the differential device and configured to be fitted to and mounted on one vehicle-width-direction side of the oil pan, wherein a fitting portion that is formed in a cylindrical shape is provided in the differential housing, a fitted portion that is formed in a cylindrical shape and to which the fitting portion of the differential housing is fitted is provided in the oil pan, a fitting face portion (43a, 75a) of one of the fitting portion of the differential housing and the fitted portion of the oil pan is fitted to a fitting face portion (43a, 75a) of the other of the fitting portion of the differential housing and the fitted portion of the oil pan, the fitting face portion of the differential housing is formed by an outer peripheral face of the fitting portion of the differential housing, the fitting face portion of the oil pan is formed by an inner peripheral face of the fitted portion of the oil pan, and an outer diameter of the fitting face portion of the differential housing is formed so as to be smaller than an inner diameter of the fitting face portion of the oil pan, characterized in that the fitting face portion (43a, 75a) of the one of the fitting portion of the differential housing and the fitted portion of the oil pan comprises, at different positions in a circumferential direction, a plurality of recesses recessed in a radial direction and a plurality of projections protruding in the radial direction, and is fitted to the fitting face portion (43a, 75a) of the other of the fitting portion of the differential housing and the fitted portion of the oil pan by the plurality of projections.