of the electric motor 74 is transmitted through the primary shaft 78 the drive gear 84 the driven gear 94 the secondary shaft 88 the final drive gear 96 to the differential unit 62 thereby driving the drive wheels not shown through the drive shafts 70 and 72 when the clutch 6 is engaged in this case the drive force of the engine 2 is added to the drive force of the electric motor 74 thereby obtaining a large drive torque when the clutch 6 is disengaged the vehicle is driven by the drive force of the electric motor 74 only that is the previous motor driven condition of the vehicle is restored in the case of canceling the running by the electric motor 74 the rotational direction of the motor 100 is reversed to clockwise rotate the one way camshaft 104 thereby clockwise rotating the one way cam 108 to the neutral condition shown in fig5 b as a result the cam follower 116 is moved in the direction opposite to the direction of the arrow 140 thereby disengaging the synchronozer sleeve 86 a from the drive gear 84 accordingly the drive gear 84 becomes rotatable relative to the primary shaft 78 so that the drive force of the electric motor 74 is not transmitted to the secondary.