An abnormality diagnosis apparatus includes a power consumption estimation section that estimates power consumption of a motor, which is driven by power supplied from a power supply, and power consumption of an auxiliary unit using the power to calculate a power consumption estimate value, a power-supply voltage estimation section that calculates a power-supply voltage estimate value, which is an estimate value of voltage of the power supply, based on the power consumption estimate value and a power-supply current detection value, which is based on a detection value of a power-supply current sensor detecting a current of the power supply, and an abnormality determination section that determines an abnormality of a power-supply voltage sensor detecting a voltage of the power supply, based on a comparison result between the power-supply voltage estimate value and a power-supply voltage detection value, which is based on a detection value of the power-supply voltage sensor.