This in-wheel motor drive device 21 is provided with: an electric motor 22 for driving a wheel; a speed reducer 23 for reducing the speed of the electric motor 22 and outputting the reduced speed; a bearing 24 for the wheel, which transmits the output of the speed reducer 23 to the wheel; and a casing 25 for accommodating the speed reducer 23. The speed reducer 23 has a structure in which an intermediate gear 33 is rotatably supported by a rolling bearing 41 relative to the casing 25. The flange 54 of the intermediate gear 33 having a tooth tip outer diameter greater than the outer-ring outer diameter of the rolling bearing 41 is disposed in the narrow space between the facing wall surfaces of the casing 25, and the flange 54 of the intermediate gear 33 is provided with an oil passage hole 55 extending from one wall surface side of the casing 25 toward the rolling bearing 41 located on the other wall surface side.