Provided is an apparatus for operating interior permanent magnet synchronous motor by receiving a first current command of a flux weakening control region I in a system including a detector measuring a position and a speed of a rotor of an IPMSM, the apparatus including a feedback unit transmitting over-modulated voltage information to a correction unit, the correction unit using the rotor speed and the over-modulated voltage information to correct the first current command to a second current command of a flux weakening control region II, a control unit controlling the second current command to output a voltage, a first limit unit limiting an output of the control unit to a maximum voltage synthesizable by an inverter unit, and the inverter unit applying a 3-phase voltage command for following a command torque to the IPMSM using an output of a voltage limit unit.