In a power unit device of a vehicle in which a differential device is arranged on one side of an engine, warming-up of the engine is facilitated while heat convection from an oil pan to a differential housing is inhibited. The power unit device includes a heat insulating member that covers the outer side of an oil pan, and a differential housing that is fitted to and mounted on the oil pan. A fitting portion is provided in the differential housing, and a fitted portion is provided in the oil pan. A fitting face portion of one of the fitting portion and the fitted portion includes, at different positions in the circumferential direction, a plurality of recesses and projections in the radial direction, and is fitted to a fitting face portion of the other of the fitting portion and the fitted portion by the plurality of projections.