An electric-power control device (10, 10A to 10E) which drives an electric motor including a rotor into which a rotation shaft is inserted and a stator provided on an outer peripheral side of the rotor, the electric-power control device (10, 10A to 10E) comprising: an annular substrate (5, 5B, 5C) including a through hole through which the rotation shaft passes, the substrate (5, 5B, 5C) being provided to face the rotor and the stator; a connector which is provided at a peripheral portion of the substrate (5, 5B, 5C), and to which a lead wire is connected; a power semiconductor module (11, 111) mounted on a first region which is one of sides of the substrate (5, 5B, 5C) which are divided with respect to a straight line connecting a center of the through hole to a center of the connector, the power semiconductor module (11, 111) including a ground terminal and a driving circuit; and a microcomputer mounted on a second region which is an other of the sides of the substrate (5, 5B, 5C), the microcomputer including a ground terminal and being configured to control electric power to be supplied to the electric motor, on the substrate (5, 5B, 5C), a first ground pattern portion (11a, 11b), a second ground pattern portion (12a, 12b) are provided, the first ground pattern portion (11a, 11b) being provided as a ground electrode which is connected to the ground terminal of the power semiconductor module (11, 111), and formed to extend from the power semiconductor module (11, 111) toward the connector in the first region, the second ground pattern portion (12a, 12b) being provided as a ground electrode which is separated from the first ground pattern portion (11a, 11b), connected to the ground terminal of the microcomputer, and formed to extend from the microcomputer toward the connector in the second region, a connection portion (20, 120, 220) connecting a part of the first ground pattern portion (11a, 11b) and a part of the second ground pattern portion (12a, 12b), wherein a length of the first ground pattern portion (11a, 11b) and the second ground pattern portion (12a, 12b) is longer than a straight line distance between the power semiconductor module (11, 111) and the microcomputer. an annular substrate (5, 5B, 5C) including a through hole through which the rotation shaft passes, the substrate (5, 5B, 5C) being provided to face the rotor and the stator; a connector which is provided at a peripheral portion of the substrate (5, 5B, 5C), and to which a lead wire is connected; a power semiconductor module (11, 111) mounted on a first region which is one of sides of the substrate (5, 5B, 5C) which are divided with respect to a straight line connecting a center of the through hole to a center of the connector, the power semiconductor module (11, 111) including a ground terminal and a driving circuit; and a microcomputer mounted on a second region which is an other of the sides of the substrate (5, 5B, 5C), the microcomputer including a ground terminal and being configured to control electric power to be supplied to the electric motor, on the substrate (5, 5B, 5C), a first ground pattern portion (11a, 11b), a second ground pattern portion (12a, 12b) are provided, the first ground pattern portion (11a, 11b) being provided as a ground electrode which is connected to the ground terminal of the power semiconductor module (11, 111), and formed to extend from the power semiconductor module (11, 111) toward the connector in the first region, the second ground pattern portion (12a, 12b) being provided as a ground electrode which is separated from the first ground pattern portion (11a, 11b), connected to the ground terminal of the microcomputer, and formed to extend from the microcomputer toward the connector in the second region, a connection portion (20, 120, 220) connecting a part of the first ground pattern portion (11a, 11b) and a part of the second ground pattern portion (12a, 12b), wherein a length of the first ground pattern portion (11a, 11b) and the second ground pattern portion (12a, 12b) is longer than a straight line distance between the power semiconductor module (11, 111) and the microcomputer.