An automotive generator/motor is driven by a battery via an inverter. Resistance 2Ra0 is expressed by 2Ra0=Vmax/ {square root over (3)} Iamax, where Vmax is a maximum voltage applicable across any two terminals from the inverter and Iamax is a maximum current which must be fed from the inverter into each of the terminals when the maximum voltage Vmax is applied for maximizing torque produced by the automotive generator/motor at a power factor of 1 under voltage saturation conditions, and the armature winding is configured such that resistance 2Ra across any two terminals satisfies a relationship expressed by 0.8Ra0.ltoreq.2Ra.ltoreq.3.8Ra0.