A variable-speed speed increaser includes: an electric driving device that generates a rotational driving force; and a transmission device that changes the speed of the rotational driving force generated by the electric driving device and transmits the changed rotation driving force to a driving target. The transmission device includes: a sun gear; a sun gear shaft fixed to the sun gear; a planetary gear that meshes with the sun gear; an internal gear; a planetary gear carrier that has a planetary gear carrier shaft; and an internal gear carrier that has an internal gear carrier shaft. The electric driving device includes: a constant-speed motor that has a constant-speed rotor; and a variable-speed motor that has a variable-speed rotor. The internal gear carrier includes a clutch mechanism that connects a cylindrical portion connected to the internal gear with the internal gear carrier shaft.