PURPOSE: To evaluate the durability of a hole making drill properly and automatically by setting the vicinity of the drilling position by a hole making drill for an elastic foamed body, at a measurement position, detecting the displacement quantity of the elastic foamed body at the measurement position in drilling by a displacement sensor, and judging the endurance limit of the twist drill.

CONSTITUTION: When drilling is carried out on a polyurethane foamed body 10 by a motor-driven type drill 20, the displacement at the upper part approach position (measurement position) M at the drilling position by the drill 20 is detected by a displacement detector 30 including a laser type displacement sensor, and the result is recorded in a recording device 40. In the drilling work, the spot of the laser type displacement sensor is allcwed to coincide with the measurement position M in the vicinity of the upper part of the drill insertion position, and drilling is started in this state, and the displacement at the measurement position M of the foamed body 10 is detected continuously. The signal based on the displacement quantity is converted to the voltage signal, and compared with the upper limit value, and when the state where the voltage signal exceeds the upper limit value is generated three times continuously, the reach to the endurance limit is judged.