A field winding synchronous generator-motor includes: a power conversion section that is connected to an electric rotating machine and operating as a generator-motor, and that controls the electric rotating machine; a compensation amount storage section that stores a compensation capable of improving characteristics of the electric rotating machine from a reference position of a rotor; a positional compensation operation section that makes a compensation operation of positional information from a rotor position and a value of the compensation amount storage section; a conducting phase storage section that stores a conducting phase to each armature winding from the reference position; and a rectangular wave application voltage command section that commands a rectangular wave application voltage to each armature winding with respect to the power conversion section from a value of the positional compensation operation section and a value of the conducting phase storage section.