A variable speed accelerator is provided, including an electric driving device generating a rotational driving force, and a planetary gear transmission device changing the speed of the rotational driving force and transmitting the changed rotation driving force to a driving target. The electric driving device includes: a variable-speed motor having a variable-speed rotor connected to a variable-speed input shaft of the transmission device; and a constant-speed motor having a constant-speed rotor connected to a constant-speed input shaft of the transmission device. The variable-speed rotor and the planetary gear carrier shaft have a shaft insertion hole formed to pass therethrough in the axial direction.