In a vehicular electric power generation apparatus having an a.c. generator (1) and an engine (2), a rotation speed (N1) of the a.c. generator (1) at the idling rotation operation of the engine (2) is set to be higher than a rotation speed (Np), at which the driving torque of the a.c. generator (1) becomes a maximum (Tp). Thus, the rotation speed of the a.c. generator (1) does not changes through the rotation speed (Np) at which the driving torque of the vehicle a.c. generator (1) becomes a maximum, even when the rotation speed of the engine (2) is raised high for running of a vehicle. Thus, changes in the load applied to the engine (2) can be restricted.