To provide a motor-driven refrigerating cycle device capable of effectively cooling an inverter part, in particular, a smooth capacitor even with a simple and compact structure.

Though the inverter part 5 is fixed on a motor housing 4 to shorten the wiring and to miniaturize the device, the smooth capacitor 55 can be effectively cooled by a low pressure refrigerant flowing in a slot 511 of a base plate 51 by fixing a case 551 of the smooth capacitor 55 to the base plate 51 for mounting circuit parts of the inverter part 5, through a high thermal conductive member 52, whereby the smooth capacitor 55 can be prevented from being unnecessarily enlarged and lowering its electric resistance, the reliability is improved, and the device is miniaturized.