A generator having a field coil L, and an SW1 control circuit 2 for controlling field current flowing through the field coil L. When a generating operation of the generator is to be ended, a switch 1 SW1 is turned off to interrupt the field current flowing through the field coil L, and a switch 2 SW2 is turned off to allow the field current remaining the field coil L to the current path including a resistance element 1 with a resistance element capable of quickly attenuating the field current.