A motor drive device comprising: an inverter circuit (40) having a smoothing capacitor (70); a drive circuit unit (102) that outputs an operation signal to the inverter circuit; a control unit (101) that controls the drive circuit unit; and operation voltage generation units (105, 106, 107, 105A) that generate operation voltage for the drive circuit unit and the control unit and supply power to the drive circuit unit and the control unit. The inverter circuit coverts DC voltage from a first power supply (20) to AC voltage and outputs same to a motor coil having a plurality of phases. The control unit outputs signals to the drive circuit unit on the basis of a command value from a host control device that operates on power from a second power supply (21) having a lower voltage than the first power supply. The operation voltage generation units are capable of generating the operating voltage regardless of whether power is supplied by the first power supply or the second power supply.