To provide the control unit of a synchronous machine which comprises an initial magnetic pole position detecting means of a rotor, in which no position detector is used at starting and no characteristics of a motor is affected.

The control unit comprises a power converter 4 that supplies a multi-phase AC current to the armature of a synchronous machine 1, a field converter 5 that supplies a DC current to the field of the synchronous machine 1, an electrical quantity detecting means 7 for detecting the electrical quantity of the armature of the synchronous machine 1, and an initial magnetic pole position calculating means 6 in which the output of the electrical quantity detecting means 7 is inputted. The initial magnetic pole position calculating means 6 acquires the position of a rotor of the synchronous machine 1 by calculating based on the detection signal acquired from the electrical quantity detecting means 7 when the field converter 5 applies a DC current to the field.