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 including a through hole through which the rotation shaft passes, the substrate being provided to face the rotor and the stator ; a connector which is provided at a peripheral portion of the substrate , and to which a lead wire is connected; a power semiconductor module mounted on a first region which is one of sides of the substrate 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 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 , the microcomputer including a ground terminal and being configured to control electric power to be supplied to the electric motor , on the substrate , a first ground pattern portion , a second ground pattern portion are provided, the first ground pattern portion being provided as a ground electrode which is connected to the ground terminal of the power semiconductor module , and formed to extend from the power semiconductor module toward the connector in the first region, the second ground pattern portion being provided as a ground electrode which is separated from the first ground pattern portion , 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 connecting a part of the first ground pattern portion and a part of the second ground pattern portion , wherein a length of the first ground pattern portion and the second ground pattern portion is longer than a straight line distance between the power semiconductor module and the microcomputer . an annular substrate including a through hole through which the rotation shaft passes, the substrate being provided to face the rotor and the stator ; a connector which is provided at a peripheral portion of the substrate , and to which a lead wire is connected; a power semiconductor module mounted on a first region which is one of sides of the substrate 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 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 , the microcomputer including a ground terminal and being configured to control electric power to be supplied to the electric motor , on the substrate , a first ground pattern portion , a second ground pattern portion are provided, the first ground pattern portion being provided as a ground electrode which is connected to the ground terminal of the power semiconductor module , and formed to extend from the power semiconductor module toward the connector in the first region, the second ground pattern portion being provided as a ground electrode which is separated from the first ground pattern portion , 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 connecting a part of the first ground pattern portion and a part of the second ground pattern portion , wherein a length of the first ground pattern portion and the second ground pattern portion is longer than a straight line distance between the power semiconductor module and the microcomputer . <EOS>