Abstract: A voltage regulator 3 for controlling the output voltage of the AC generator 1 includes two voltage dividers having junction points J1 and J2 coupled to the zener diode 306 controlling the ON/OFF of the controlling transistor 309 and the power transistor 310. The voltage level at the junction point J1 is varied by means of the short-circuiting transistor 313 in response to the output of control transistor 401. Usually, the voltage at the junction point J1 is higher than the voltage at the junction point J2, and the output voltage of the AC generator 1 is controlled on the basis of the voltage at the junction point J1 to a normal and a reduced level in accordance with the output at the target voltage change-over terminal B. When quick charging is needed, however, the control transistor 402 is turned on to ground the junction point J1, such that the output voltage of the AC generator 1 is controlled to a higher level on the basis of the voltage at the junction point J2.