A cooling structure of a generator motor includes: a first passage provided to an end side member placed at one end of a housing of a generator motor, the first passage extending toward a rotation center axis of an input/output shaft housed in the housing, the first passage opening to a side of the input/output shaft, and the first passage including a restriction section halfway through; and a second passage provided to the end side member, branching off from the first passage at a position on an outer side in a radial direction of the input/output shaft than the restriction section and subsequently extending toward a rotor attached to an outside of the input/output shaft, and the second passage opening to a side of the rotor.