A variable-speed speed-up mechanism (1) includes an electric device (50) and a transmission device (10). In the transmission (10), an internal gear carrier shaft (37) forms a constant-speed input shaft (Ac), and a planetary gear carrier shaft (27) forms a variable-speed input shaft (Av). The electric device (50) includes a constant-speed electric motor (51) having a constant-speed rotor (52) which is configured to rotate the constant-speed input shaft (Ac), and a variable-speed electric motor (71) having a variable-speed rotor (72) which is connected to the variable-speed input shaft (Ac). The variable-speed speed-up mechanism (1) further includes a brake mechanism (200) which is configured to detect an abnormal state of the variable-speed electric motor (71), stop the rotation of at least one of the variable-speed input shaft (Ac) and the variable-speed rotor (72), and continue the rotation of the constant-speed rotor (52).