An electric power steering device, comprising: a motor ; and a control unit , which is provided side by side in a row with the motor in an axial direction of an output shaft of the motor , and is integrated with the motor , the control unit including: a power module including a plurality of switching elements configured to supply current to the motor ; a control board configured to output a control signal to each of the plurality of switching elements; a heat sink configured to allow heat radiation from the control unit ; a housing that forms an outer case of the control unit; a sensor rotor mounted to an end portion of the output shaft on the control unit side; and a rotation sensor configured to detect rotation of the sensor rotor , the heat sink including: a base portion provided on the motor side in the housing ; and a column portion extending from the base portion toward an opposite side to the motor along an extension of the output shaft , the power module and the control board being arranged, in parallel to the output shaft , in the housing , and wherein the column portion has a polygonal column shape having a plurality of mounting portions defined by flat surfaces parallel to the axial direction of the output shaft , and wherein the control board is provided on one of the plurality of mounting portions , and wherein the power module is provided on a mounting portion adjacent in a circumferential direction to the one mounting portion out of the plurality of mounting portions , and characterized in that the rotation sensor is provided in a recess formed in an opposite position to the sensor rotor of the base portion . a motor ; and a control unit , which is provided side by side in a row with the motor in an axial direction of an output shaft of the motor , and is integrated with the motor , the control unit including: a power module including a plurality of switching elements configured to supply current to the motor ; a control board configured to output a control signal to each of the plurality of switching elements; a heat sink configured to allow heat radiation from the control unit ; a housing that forms an outer case of the control unit; a sensor rotor mounted to an end portion of the output shaft on the control unit side; and a rotation sensor configured to detect rotation of the sensor rotor , a power module including a plurality of switching elements configured to supply current to the motor ; a control board configured to output a control signal to each of the plurality of switching elements; a heat sink configured to allow heat radiation from the control unit ; a housing that forms an outer case of the control unit; a sensor rotor mounted to an end portion of the output shaft on the control unit side; and a rotation sensor configured to detect rotation of the sensor rotor , the heat sink including: a base portion provided on the motor side in the housing ; and a column portion extending from the base portion toward an opposite side to the motor along an extension of the output shaft , a base portion provided on the motor side in the housing ; and a column portion extending from the base portion toward an opposite side to the motor along an extension of the output shaft , the power module and the control board being arranged, in parallel to the output shaft , in the housing , and wherein the column portion has a polygonal column shape having a plurality of mounting portions defined by flat surfaces parallel to the axial direction of the output shaft , and wherein the control board is provided on one of the plurality of mounting portions , and wherein the power module is provided on a mounting portion adjacent in a circumferential direction to the one mounting portion out of the plurality of mounting portions , and characterized in that the rotation sensor is provided in a recess formed in an opposite position to the sensor rotor of the base portion . <EOS>