An apparatus for operating an interior permanent magnet synchronous motor IPMSM by receiving a command torque to drive the IPMSM in a system including a detector measuring a position and a speed of a rotor of the IPMSM; the apparatus comprising: an output unit generating and outputting a current command driving a Maximum Torque Per Ampere (MTPA) based on the command torque; a correction unit correcting the current command outputted by the output unit; a feedback unit transmitting over-modulated voltage information to the correction unit; a control unit controlling the current command to output a voltage; a first limit unit limiting an output of the control unit using a maximum voltage synthesizable by an inverter unit ; and the inverter unit applying a 3-phase voltage command for tracking a command torque to the IPMSM using an output of the first limit unit ; the apparatus characterized in that : the output unit comprises a second limit unit limiting a size of the torque command to a predetermined maximum range and a predetermined minimum range; a first calculation unit calculating a normalized command torque by dividing an output of the second limit unit by a normalized torque; a 1-D look-up table units (43a and 43b) outputting a normalized current command by using the normalized command torque; and a second calculation units (44a and 44b) outputting a current command driving a MTPA by multiplying the normalized current command by the normalized current; wherein the correction unit comprises a processing unit correcting a current command driving the MTPA by using a unit vector maintaining a constant torque, and a third limit unit limiting the size of the current from the current command corrected by the processing unit ; wherein the third limit unit provides a priority to a d-axis current on the synchronous reference frame relative to the corrected current command, outputs the d-axis current on the priority within a size of a rated current, and selects as permissible range of a q-axis current command a balance where the size of the d-axis current is subtracted from the rated current. the output unit comprises a second limit unit limiting a size of the torque command to a predetermined maximum range and a predetermined minimum range; a first calculation unit calculating a normalized command torque by dividing an output of the second limit unit by a normalized torque; a 1-D look-up table units (43a and 43b) outputting a normalized current command by using the normalized command torque; and a second calculation units (44a and 44b) outputting a current command driving a MTPA by multiplying the normalized current command by the normalized current; wherein the correction unit comprises a processing unit correcting a current command driving the MTPA by using a unit vector maintaining a constant torque, and a third limit unit limiting the size of the current from the current command corrected by the processing unit ; wherein the third limit unit provides a priority to a d-axis current on the synchronous reference frame relative to the corrected current command, outputs the d-axis current on the priority within a size of a rated current, and selects as permissible range of a q-axis current command a balance where the size of the d-axis current is subtracted from the rated current. <EOS>