Abstract: In measuring characteristics of a device such as PRAM, inputted pulse signal is made blunt and a voltage applied to the device and a current flowing through the device cannot be precisely measured. To solve these problems, the present invention provides a resistor for making a voltage drop of a signal outputted from the pulse generator. The active differential probe outputs a signal corresponding to a potential difference between the both ends of the resistor. The signal is inputted to an oscilloscope.