A field-winding type of synchronous machine comprises a stator with an armature winding wound phase by phase, a rotor having a rotor core with a field winding wound, and a circuit enabling an armature current to pass the armature winding, the armature current corresponding to a synchronous current producing a rotation field rotating at an electrical-angle rotation speed agreeing to a rotation speed of the rotor. The synchronous machine further comprises a current suppressor and a current supplier. The current suppressor is connected to the field winging and suppresses, into a unidirectional current, an induced alternating current induced through the field winding in response to the armature current passing the armature winding. The current supplier supplies, phase by phase, to the armature winding a rotor exciting current whose waveform is different from the synchronous current only during a predetermined period of time shorter than one cycle of the synchronous current.