PURPOSE: To reduce an error of measurement with a stress measuring device, by providing a plus/minus sensitivity correcting circuit to correct the level of the detection signal of a reception processing circuit and setting both tensile stress and compression stress at the same level.

CONSTITUTION: An energizing circuit of energizing coils 31 and 32 of detection terminals consists of an oscillator 17 and a coil driver 18 and is energized by a 1kHz alternating current. A reception processing circuit which processes the induced voltage of detection coils 41 and 42 consists of a photocoupler 19, a diode driver 20, a phase controller 30, a comparator 31 and an integration circuit 32. An operator selects a set corresponding to the material of a measurement subject among sets 351W356 and sets a selector switch 34 to control a variable resistance VR of the controller 30 so as to obtain the maximum absolute value for display of a voltmeter MET. Then the foot tips of cores 1 and 2 are made touch onto the measuring point of the measurement subject, and the detection terminal is turned round the center shaft of the detection terminal. The display is read when the value of the meter MET shows the maximum and minimum values. The revolving angle obtained at that time point is read as the direction of the main stress.