This variable electric motor system comprises an electrically powered device (50) and a planet gear transmission device (10). Among a sun gear shaft (12), a planet gear carrier shaft (27), and an internal gear carrier shaft (37) of the planet gear transmission device (10), one shaft constitutes an output shaft (Ao), another shaft constitutes a constant-speed input shaft (Ac), and the remaining shaft constitutes a variable-speed input shaft (Av). The electrically powered device (50) includes: a constant-speed electric motor (51) including a constant-speed rotor (52) that rotates about the axis (Ar) thereof, and that is connected to the constant-speed input shaft (Ac); and a variable-speed electric motor (71) including a variable-speed rotor (72) that rotates about the axis (Ar) thereof, and that is connected to the variable-speed input shaft (Av). A shaft insertion hole (74) is formed in the variable-speed rotor (72) so as to penetrate the same in the axial direction, the shaft insertion hole being formed in a cylindrical shape about the axis (Ar). The constant-speed rotor (52) is passed through the shaft insertion hole (74).