A rotating side case supporting the rotor of an in-wheel motor and a wheel or a hub are interconnected by a flexible coupling which comprises a motor-side plate and a wheel-side plate having a plurality of grooves and a plurality of grooves formed on their opposed surfaces in the circumferential direction at an angle of 45.degree. from the radial direction of the plates and extending in directions orthogonal to each other, respectively, small balls sandwiched between the grooves and in such a manner that they can slide, and an intermediate plate interposed between the above plates and having guide holes for guiding the small balls in a direction orthogonal to the radial direction of the plates and which has a small number of parts and is easily assembled.