A voltage detecting device according to an aspect of embodiments includes a detecting unit and a mode switching unit. The detecting unit detects voltages of battery cells of a battery stack in which the battery cells are connected to each other. The mode switching unit switches between an active mode in which the detecting unit detects the voltages and a standby mode in which a current flowing into the detecting unit is less than a predetermined value. Moreover, the detecting unit includes a voltage detecting unit that detects the voltages of the battery cells and/or a voltage of a power supply of the detecting unit in a predetermined interval. The mode switching unit switches between the active mode and the standby mode in accordance with a timing at which the voltage detecting unit detects the voltage (s).