An in-wheel motor drive assembly 21 includes: a motor unit A; a speed reduction unit B having an output shaft 28 reducing the rotational speed of the motor rotary shaft 35 and outputting the reduced rotation and a speed-reduction-unit casing 22b forming a contour, and disposed on one axial side of the motor unit A; a wheel hub bearing unit C having a wheel hub 32 fixedly coupled with the output shaft 28 and a wheel-hub-bearing outer ring 22c rotatably supporting the wheel hub 32, and disposed on one axial side of the speed reduction unit B; and coupling portions 63, 64 secured to at least one of the wheel-hub-bearing outer ring 22c and speed-reduction-unit casing 22b to couple with members of a vehicle body.