An in-wheel motor drive unit (21) comprises a casing (22), a motor part (A), a deceleration part (B), a wheel hub (31), and a wheel hub bearing (33) rotatably supporting the wheel hub (31) with respect to the casing (22). The wheel hub bearing (33) includes first and second outer track surfaces (33a) and (33b) provided on the inner diameter surface of the casing (22), a first inner track surface (33c) provided on the outer diameter surface of a wheel-side rotation member (30) and opposed to the first outer track surface (33a), a second inner track surface (33d) provided on the outer diameter surface of the wheel hub (31) and opposed to the second outer track surface (33b), and a plurality of rolling elements (33e) arranged between the outer track surfaces (33a) and (33b) and the inner track surfaces (33c) and (33d).