Abstract: Disclosed is a motor-operated flow control valve for internal combustion engines which has a longer useful life and does not cause a drop of torque generated by a motor at the start-up. A rotor shaft (9) is reciprocated with rotating motion of a motor (32), whereupon a valve head (2a) is moved to open and close an orifice for control of a flow rate. Specific frequency of a rotor unit (33) of the motor (32) is set to be higher than the secondary vibration frequency of rotation of a 4-cycle internal combustion engine. The rotor unit (33) comprises an integral magnet (25), a single ball bearing (27) and a resin-made magnet holder (26) for supporting these two members, the magnet, the ball bearing and the magnet holder being formed into an integral structure. The rotor unit is supported such that an outer race (27c) of the ball bearing (27) is held at its one end against an inner peripheral wall of a housing resin (14) and a preload is applied to the other end of the outer race (27c).