PURPOSE: To enable measurement of the mechanical properties of an object to be inspected without destructing said object by magnetizing alternately a ferromagnetic material from the outside and measuring the delay time of magnetization with respect to a change in the magnetic field or measuring the difference between said delay time and the delay time of the magnetization of a reference sample.

CONSTITUTION: The excitation current outputted by an amplifier 5 is applied to an excitation coil 61 of a detecting end 6 and is grounded through a resistor 7. The voltage of the registor 7 on the side connected to the coil is converted via an amplifier 51 to a square wave by the 1st comparator 9. On the other hand, the output voltage from a detecting coil 63 obtd. by bringing an object to be measured into contact with the end 6 is converted to a square wave by the 2nd comparator 10. When the square waves of the equal amplitude obtd. from the 1st and 2nd comparators 9, 10 are put into an antiphase adder 11, positive or negative square pulses are generated only during the time when the phases of both square waves are different. Such pulses are inputted to a switching gate 12 and when the output pulses from a frequency divider 2 are inputted to the other input end, clock pulses are passed and outputted only during the pulse width time of the phase difference. The pulses are counted with a counter 13 and are displayed on an LED display device 15.