PURPOSE: To perform voltage measurement down to a low frequency without the delay of a display result, by decreasing the time constant of a smoothing circuit while a range switching signal is being outputted.

CONSTITUTION: A voltage to be measured, applied to an input terminal 111, is supplied to an AD converter 118 through an automatic range switching circuit 112, a rectifying circuit 116, and a smoothing circuit 117 to display its AD conversion output on a display device 119. The automatic range switching circuit 112 is switched under the control of a control circuit 115 supplied with an overflow signal 121 and a range switching-down signal 122. On the other hand, every time ranges are switched, a switching means 211 turns on as long as a time determined by the pulse width of a range switching signal 212, decreasing the time constant of the smoothing circuit 177. Consequently, even if a rectification output voltage varies stepwise owing to the range switching, the output voltage of the smoothing circuit is varied following up its stepwise variations.