An apparatus for measuring voltage is provided which measures output voltage between at least one pair of detecting terminals provided on an object under measurement. The apparatus for measuring voltage includes a first connecting terminal connected to one of the at least one pair of detecting terminals, a second connecting terminal connected to the other of the at least one pair of detecting terminals, a capacitor connected between the first connecting terminal and the second connecting terminal, a voltage detecting means for measuring voltage of the capacitor, and a pre-charging means for pre-charging the capacitor with predetermined voltage out of range of voltage which the object under measurement can output to the at least one pair of detecting terminals.