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 (6a, 6b) 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 (6a, 6b) 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 (8d, 8e, 8f, 8g) 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 (8d, 8e, 8f, 8g), and wherein the power module (6a, 6b) is provided on a mounting portion (8e, 8f) adjacent in a circumferential direction to the one mounting portion out of the plurality of mounting portions (8d, 8e, 8f, 8g), 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 (6a, 6b) 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 (6a, 6b) 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 (6a, 6b) 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 (8d, 8e, 8f, 8g) 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 (8d, 8e, 8f, 8g), and wherein the power module (6a, 6b) is provided on a mounting portion (8e, 8f) adjacent in a circumferential direction to the one mounting portion out of the plurality of mounting portions (8d, 8e, 8f, 8g), 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.