Motor drive device configured to detect capacitor deterioration and to restrict a motor based upon the detected deterioration

A motor drive device includes a storage unit that stores an initial value of a static capacitance correlation value of a static capacitance of a smoothing capacitor in an initial state, when the smoothing capacitor is connected to an inverter. A measurement unit of the motor drive device includes a timing generation circuit and a calculation unit. The measurement unit measures the static capacitance correlation value of the smoothing capacitor as a measured value at a time after the initial state. A determination unit of the motor drive device determines whether there is deterioration in the smoothing capacitor based on a relationship between the measured value and the initial value. A restrictor of the motor drive device restricts a maximum rotation number of a motor when capacitor deterioration is determined, thereby reducing a ripple current, limiting heat generation in the capacitor, and extending the product life of the capacitor, without increasing the number of parts in the motor drive device.