An in-wheel motor drive device, comprising: a wheel hub bearing unit adapted to rotatably support a wheel hub extending in a vehicle width direction; a motor unit adapted to drive the wheel hub; and a speed reducer unit adapted to reduce an output rotation of the motor unit and transmit this to the wheel hub bearing unit, wherein the speed reducer unit includes: an input shaft adapted to couple to a motor rotating shaft of the motor unit; an output shaft adapted to couple to the wheel hub and extend parallel to the input shaft; a first and a final intermediate shafts (35, 38) extending parallel to the input shaft and the output shaft; an input gear adapted to couple to the input shaft; an output gear adapted to couple to the output shaft; and a plurality of intermediate gears (34, 36, 37, 39) adapted to couple to the first and the final intermediate shafts (35, 38), the input gear, the plurality of intermediate gears (34, 36, 37, 39), and the output gears meshing with each to configure a drive transmission path leading to the output gear from the input gear through the plurality of intermediate gears (34, 36, 37, 39), wherein the first intermediate shaft is disposed above and adjacent to the input shaft and is supplied with driving torque from the input shaft, and the final intermediate shaft is disposed above and adjacent to the output shaft and supplies driving torque to the output axis, wherein an axis of the input shaft, an axis (Nl) of the final intermediate shaft, and an axis of the output shaft are disposed in this order in a front-to-rear direction of a vehicle, and axes (Nl, Nf) of the first and the final intermediate shafts (35, 38) are disposed above the axis of the input shaft and the axis of the output shaft, wherein the axis of the output shaft, the axis (Nf) of the first intermediate shaft, the axis (Nl) of the final intermediate shaft, and the axis of the input shaft each extend in the vehicle width direction, and the input shaft, the first intermediate shaft, the final intermediate shaft, and the output shaft, as viewed from an axial direction, are arranged to have a reference line successively connecting the axis of the input shaft, the axis (Nf) of the first intermediate shaft, the axis (Nl) of the final intermediate shaft, and the axis of the output shaft, draw an in-verted U-shape. a wheel hub bearing unit adapted to rotatably support a wheel hub extending in a vehicle width direction; a motor unit adapted to drive the wheel hub; and a speed reducer unit adapted to reduce an output rotation of the motor unit and transmit this to the wheel hub bearing unit, wherein the speed reducer unit includes: an input shaft adapted to couple to a motor rotating shaft of the motor unit; an output shaft adapted to couple to the wheel hub and extend parallel to the input shaft; a first and a final intermediate shafts (35, 38) extending parallel to the input shaft and the output shaft; an input gear adapted to couple to the input shaft; an output gear adapted to couple to the output shaft; and a plurality of intermediate gears (34, 36, 37, 39) adapted to couple to the first and the final intermediate shafts (35, 38), the input gear, the plurality of intermediate gears (34, 36, 37, 39), and the output gears meshing with each to configure a drive transmission path leading to the output gear from the input gear through the plurality of intermediate gears (34, 36, 37, 39), wherein the first intermediate shaft is disposed above and adjacent to the input shaft and is supplied with driving torque from the input shaft, and the final intermediate shaft is disposed above and adjacent to the output shaft and supplies driving torque to the output axis, wherein an axis of the input shaft, an axis (Nl) of the final intermediate shaft, and an axis of the output shaft are disposed in this order in a front-to-rear direction of a vehicle, and axes (Nl, Nf) of the first and the final intermediate shafts (35, 38) are disposed above the axis of the input shaft and the axis of the output shaft, wherein the axis of the output shaft, the axis (Nf) of the first intermediate shaft, the axis (Nl) of the final intermediate shaft, and the axis of the input shaft each extend in the vehicle width direction, and the input shaft, the first intermediate shaft, the final intermediate shaft, and the output shaft, as viewed from an axial direction, are arranged to have a reference line successively connecting the axis of the input shaft, the axis (Nf) of the first intermediate shaft, the axis (Nl) of the final intermediate shaft, and the axis of the output shaft, draw an in-verted U-shape.