A system for controlling a synchronous motor is provided with a detector (112) detecting the rotational angle of a synchronous motor (101), and a control circuit (108) which generates a sine value corresponding to the rotational angle detected by the detector (112) and multiples an effective value current command by that sine value, a multiplication output from the control circuit (108) being applied as a current command value to an armature winding of the synchronous motor (101). In this case, the control circuit (108) is adapted to compensate for the detected rotational angle by the actual velocity of the synchronous motor (101), or by a command velocity given to the synchronous motor.