PURPOSE: To achieve simplification of work when a voltage value is decided by determining the voltage with a circuit of a simple structure without using a multicircuit tester or the like.

CONSTITUTION: AC voltage as object desired to decide a voltage is brought in to generate a DC voltage for measurement by rectification and smoothing with a rectification smoothing circuit 1, and when the DC voltage to be outputted from the rectification smoothing circuit 1 is higher than the first set voltage preset, the voltage is detected with a 100V decision circuit 2 to light and drive a lamp 13 on the high voltage side. When the DC voltage to be outputted from the rectification smoothing circuit 1 is lower than the second set voltage preset, the voltage is detected with a 24V decision circuit 3 to light and drive a lamp 19 on the low voltage side.