PURPOSE: To enable accurate measurement by selectively operating through the construction that the inner race of the meter unit is made free and fixed, and making the initial condition of measurement the same.

CONSTITUTION: First, when this measuring unit is mounted on the measured tape recorder, the inner race 8 of the meter unit 9 is free and the zero point of the scale 14 of the outer race 7 and the pointer 15 of the inner race 8 are completely in agreement. When the tape recorder is at play mode and the depression pin 31 is pushed, the tape T slightly runs for the moment, and the centering between the inner race 8 and the outer race 7 is automatically made. Then, the inner race 8 shows fixed state and the pointer 15 turns along the scale of the outer race 7, and finally, the drive torque by the cooperation of the capstan 25 and the pinch roller 26, that is, true tensile strength added to the tape T is displayed.