An in-wheel motor system, wherein the non-rotating side case of a motor and a knuckle are connected to each other by a motor attachment plate (11), a knuckle attachment place (12), and a damper (16) for interconnecting these plates (11) and (12), moving in the vertical direction of a vehicle. A first direct-acting guide (13) consisting of a linear bearing (13A) and a rod (13B) and a second direct-acting guide (14) consisting of a linear bearing (14A) and a rod (14B) are integrally attached to an attachment member (12m) installed on the side face of the knuckle attachment plate (12). Also, spring members (15) and (15) are installed between receiving members (11m) and (11m) for supporting both ends of the rod (14B) of the second direct-acting guide (14) installed on the motor attachment plate (11) and the fixing portion (12k) for fixing the second direct-acting guide 14 of the attachment member (12m). Thus, the rigidity of a buffer mechanism float mounting the in-wheel motor to a part around the wheel of the vehicle can be increased.