A vehicular AC electric generator configured to be used for car engine start, comprising: a rotary electric machine that has a stator and a rotor; an electric power conversion unit that has a three-phase bridge circuit having arms each of which is constituted with semiconductor switches having first main terminals, second main terminals, and control terminals; and a control circuit that controls operations of the semiconductor switches of the three-phase bridge circuit, wherein DC power from a DC power supply is converted to AC power by the three-phase bridge circuit that is controlled by the control circuit for electric power to be supplied to the rotary electric machine and the rotary electric machine to be operated as an electric motor, AC power that is generated in the rotary electric machine which is driven is converted into DC power by the three-phase bridge circuit controlled by the control circuit for electric power to be supplied to the DC power supply and the rotary electric machine to be operated as an electric power generator, control is performed by a one-pulse energization control with an energization angle in synchronization with an electrical angle cycle of the rotor when the rotary electric machine is operated as the electric motor, the stator of the rotary electric machine is configured to have a plurality of sets of three-phase windings, and the electric power conversion unit is configured to have a plurality of sets of three-phase bridge circuits (21 and 22) corresponding to the plurality of sets of three-phase windings, each of the three-phase windings of the stator is connected to the DC power supply via the corresponding three-phase bridge circuits (21, 22) of the electric power conversion unit, the plurality of sets of three-phase bridge circuits (21 and 22) are controlled to be at different switching timings from each other, characterized in that the vehicular AC electric generator is configured such that a surge voltage is generated when the semiconductor switch is turned off; the surge voltage is suppressed by avalanche breakdown, and the semiconductor switch constituting each arm in the plurality of sets of three-phase bridge circuits (21 and 22) is configured to be a one-chip MOSFET without parallel connection of power semiconductor switches. a rotary electric machine that has a stator and a rotor; an electric power conversion unit that has a three-phase bridge circuit having arms each of which is constituted with semiconductor switches having first main terminals, second main terminals, and control terminals; and a control circuit that controls operations of the semiconductor switches of the three-phase bridge circuit, wherein DC power from a DC power supply is converted to AC power by the three-phase bridge circuit that is controlled by the control circuit for electric power to be supplied to the rotary electric machine and the rotary electric machine to be operated as an electric motor, AC power that is generated in the rotary electric machine which is driven is converted into DC power by the three-phase bridge circuit controlled by the control circuit for electric power to be supplied to the DC power supply and the rotary electric machine to be operated as an electric power generator, control is performed by a one-pulse energization control with an energization angle in synchronization with an electrical angle cycle of the rotor when the rotary electric machine is operated as the electric motor, the stator of the rotary electric machine is configured to have a plurality of sets of three-phase windings, and the electric power conversion unit is configured to have a plurality of sets of three-phase bridge circuits (21 and 22) corresponding to the plurality of sets of three-phase windings, each of the three-phase windings of the stator is connected to the DC power supply via the corresponding three-phase bridge circuits (21, 22) of the electric power conversion unit, the plurality of sets of three-phase bridge circuits (21 and 22) are controlled to be at different switching timings from each other, characterized in that the vehicular AC electric generator is configured such that a surge voltage is generated when the semiconductor switch is turned off; the surge voltage is suppressed by avalanche breakdown, and the semiconductor switch constituting each arm in the plurality of sets of three-phase bridge circuits (21 and 22) is configured to be a one-chip MOSFET without parallel connection of power semiconductor switches.