To provide a vector controller of a synchronous motor structured to obtain maximum output or maximum torque within a range of a predetermined armature current irrespective of rotational speed.

The vector controller of the synchronous motor controls an armature current and a field current by a power converter treating the magnetic flux and a current of a field-winding type synchronous motor as vectors. In this controller, a vector calculator 32, an absolute value calculator 33 of rotational speed, and first and second switches 34, 35 are provided in a magnetic flux calculator 1A. During the low speed rotation of the motor, a steady value of an armature current component parallel to an air gap magnetic flux vector is controlled to zero. During the high speed rotation of the motor, the steady value of the armature current component parallel to an armature interlinkage-flux vector is controlled to zero.