To provide an internal combustion engine starting system capable of reducing the noise when starting and shortening the starting time and suitable for a vehicle stopping the idle operation.

This internal combustion engine starting system is provided with an output shaft 9a for outputting the rotation of a motor 1 through a reduction gear mechanism 9, a rotor 12 to be integrally rotated with the output shaft 9a, a driving member 10 installed in the motor 1 freely rotated and connected to a crank shaft of the internal combustion engine through a rotation transmitting member, a movable element 13 interposed between the driving member 10 and the rotor 12 and fitted to the rotor 12 freely moved in the axial direction and having a surface opposite to the axial surface of the driving member, an exciting coil 15 for exciting the driving member 10, an electromagnetic clutch 18 provided in each opposite surface of the driving member 10 and the movable element 13 and formed of torque transmitting surfaces 10a and 13a brought in pressure-contact with each other by electrifying the exciting coil 15, and a control device for electrifying the exciting coil 15 and the motor 1 in the predetermined order and for stopping the electrifying.