A voltage detecting device for an on-vehicle high-voltage battery in which secondary batteries are connected in series, the on-vehicle high-voltage battery being divided into blocks each including at least one secondary battery, includes: voltage detecting means each assigned to each block for detecting a voltage of each secondary battery included in the block; and control means for controlling the voltage detecting means, wherein a common secondary battery is selected from the secondary batteries, a voltage of the common secondary battery being detectable by two voltage detecting means, wherein the control means causes the two voltage detecting means to detect the voltage of the common secondary battery, computes a detection error between the two voltage detecting means from the detected voltage values of the common secondary battery, and makes corrections in voltage values detected by the two voltage detecting means on the basis of the computed detection error.