A voltage sensor diagnostic device comprising: a monitoring device for diagnosing a normality/abnormality of a voltage sensor configured to detect a circuit voltage in a system circuit of an electrical equipment system, the circuit voltage in the system circuit being a DC voltage, wherein: the monitoring device includes a main multiplier circuit configured to receive, as input, the circuit voltage as a monitoring voltage and output a gain-non-inverted signal as a detected value of the circuit voltage, a subordinate multiplier circuit configured to receive, as input, the circuit voltage as the monitoring voltage and output a signal that is gain-inverted with respect to the output signal from the main multiplier circuit as the detected value of a circuit voltage, and an abnormality diagnosis circuit configured to diagnose abnormalities in the main multiplier circuit and the subordinate multiplier circuit, which are the voltage sensors, based on a gain-non-inverted output signal from the main multiplier circuit and a gain-inverted output signal from the subordinate multiplier circuit; and the abnormality diagnosis circuit is configured to convert the gain-non-inverted output signal from the main multiplier circuit into a main monitoring voltage, convert the gain-inverted output signal from the subordinate multiplier circuit into a subordinate monitoring voltage, and diagnose an abnormality in the main multiplier circuit and the subordinate multiplier circuit when an absolute value of a difference between the main monitoring voltage and the subordinate monitoring voltage exceeds a difference diagnosis threshold, characterized in that an output characteristic of the main multiplier circuit is set to a characteristic having a reference gain that passes through a zero voltage point and a maximum voltage point of the main multiplier circuit output, and an output characteristic of the subordinate multiplier circuit is set to a characteristic in which an offset is added to a dead zone region in which a subordinate multiplier circuit output is small by setting an absolute value of the gain to be smaller than the reference gain. the monitoring device includes a main multiplier circuit configured to receive, as input, the circuit voltage as a monitoring voltage and output a gain-non-inverted signal as a detected value of the circuit voltage, a subordinate multiplier circuit configured to receive, as input, the circuit voltage as the monitoring voltage and output a signal that is gain-inverted with respect to the output signal from the main multiplier circuit as the detected value of a circuit voltage, and an abnormality diagnosis circuit configured to diagnose abnormalities in the main multiplier circuit and the subordinate multiplier circuit, which are the voltage sensors, based on a gain-non-inverted output signal from the main multiplier circuit and a gain-inverted output signal from the subordinate multiplier circuit; and a main multiplier circuit configured to receive, as input, the circuit voltage as a monitoring voltage and output a gain-non-inverted signal as a detected value of the circuit voltage, a subordinate multiplier circuit configured to receive, as input, the circuit voltage as the monitoring voltage and output a signal that is gain-inverted with respect to the output signal from the main multiplier circuit as the detected value of a circuit voltage, and an abnormality diagnosis circuit configured to diagnose abnormalities in the main multiplier circuit and the subordinate multiplier circuit, which are the voltage sensors, based on a gain-non-inverted output signal from the main multiplier circuit and a gain-inverted output signal from the subordinate multiplier circuit; and the abnormality diagnosis circuit is configured to convert the gain-non-inverted output signal from the main multiplier circuit into a main monitoring voltage, convert the gain-inverted output signal from the subordinate multiplier circuit into a subordinate monitoring voltage, and diagnose an abnormality in the main multiplier circuit and the subordinate multiplier circuit when an absolute value of a difference between the main monitoring voltage and the subordinate monitoring voltage exceeds a difference diagnosis threshold, convert the gain-non-inverted output signal from the main multiplier circuit into a main monitoring voltage, convert the gain-inverted output signal from the subordinate multiplier circuit into a subordinate monitoring voltage, and diagnose an abnormality in the main multiplier circuit and the subordinate multiplier circuit when an absolute value of a difference between the main monitoring voltage and the subordinate monitoring voltage exceeds a difference diagnosis threshold, characterized in that an output characteristic of the main multiplier circuit is set to a characteristic having a reference gain that passes through a zero voltage point and a maximum voltage point of the main multiplier circuit output, and an output characteristic of the subordinate multiplier circuit is set to a characteristic in which an offset is added to a dead zone region in which a subordinate multiplier circuit output is small by setting an absolute value of the gain to be smaller than the reference gain.