PURPOSE: To facilitate the measurement of wide-band characteristics and the high accuracy measurement of DC at the same time by one probe without exerting adverse effect on a system to be measured.

CONSTITUTION: A dual pass amplifier circuit is constituted of a wide-band voltage amplifier 9, an input terminal resistor 6, an imagenary earth return amplifier 21 and attenuators 4, 5. This circuit keeps the input impedance of a measuring system constant and both of the high accuracy measurement of DC and the measurement of wide-band characteristics are enabled by one probe. The high accuracy measurement of DC can be performed before and behind the attenuators and a wide-band signal and a DC signal can be outputted as a composite signal individually or in combination. Further, this circuit is equipped with a calibration offset for setting off the DC components of an input signal by a DC power supply.