A transmission-ratio-varying steering apparatus has a control circuit capable of storing a rotation angle between input and output shafts in a non-volatile memory when the generator outputs a surge voltage. The transmission-ratio-varying steering apparatus includes clamp means provided between a battery and generator on one side and a power-supply circuit on the other side. The clamp means clamps a surge voltage generated by the generator to a third predetermined voltage higher than a first predetermined voltage but lower than a second predetermined voltage. If a surge voltage higher than the second predetermined voltage is generated by the generator, a self-protection function of the power-supply circuit can be prevented from cutting off power being supplied to a microcomputer and an EEPROM.