PURPOSE: To measure a phase accurately and stably by measuring a pulse wave having the pulse width according to the phase difference between the converted square wave voltage of sine wave voltage impressed to a body to be inspected and the square wave voltage of a current passing through the body to be inspected by means of using a reference clock generator.

CONSTITUTION: The sine wave voltage A generated in a synthesizer 1 and impressed to the body 2 to be inspected is converted to the square wave B by a comparator 3 and supplied to the set input S of an FF6, and the current passing through the body 2 to be inspected is converted to the square wave C by a current/voltage converter 4 and supplied to the set input S an FF7. The output E of the FF 6 is inputted to the reset input R of the FF 7 and the outputs E,F of the FF 6,7 are supplied to the set input S and reset input R of an FF 8. The output G of the FF 8 is inputted to an AND gate 10 togethre with the reference clock signal H of the reference clock generator 9, and an gate output I is counted by a counter 11 and inputted to an input/output device 12. The phase characteristic of the body to be inspected can be thus measured accurately and stably.