PURPOSE: To perform an accurate and easy test by equipping a hydraulic cylinder at the projection part of a locking bolt embedded in a rock bed, operating the hydraulic cylinder through a portable quantitative discharge type hydraulic unit, and then recording variation in hydraulic pressure when said bolt is extracted.

CONSTITUTION: A center hole 13 is made in the center of a hydraulic cylinder 12, and the projection part of a locking bolt 2 embedded in a rock bed is run in the center hole 13; and a nut 6 is turned up around the bolt 2 to press the cylinder 12 through a spacer 10, and the cylinder 12 is put in operation by the pressurized oil of a portable quantitative discharge type hydraulic unit 14, thereby recording variation in hydraulic pressure when the bolt 2 is extracted through the nut 6 on a portable pen-drawing oscillograph 15. The variation in hydraulic pressure is recorded in waveforms AWE; the waveform A shows that a filler is hard and the locking bolt is not extracted and broken, and the waveforms AWE show that the filler is soft.