PURPOSE: To carry out the loading test accurately and easily without disturbing the soft ground by pressure-injecting a liquid between a thin inner tube which consists of stainless steel and an outer tube which consists of urethane rubber, and measuring the liquid injection amount and the liquid pressure.

CONSTITUTION: A boring hole for test is cut, a loading test device is laid, and the lower side of a piston 38 is contacted closely to the bottom of the hole. Then, a probe main body made by covering an inner tube 10 which consists of a thin structure of a solid material by an outer tube 12 which consists of a rubber elastic material is inserted in the ground. Then a motor-deceleration device 22 is driven to push down a cylinder 20 to pressurize the water. Moreover, the water of a pressured liquid is poured between the inner tube 10 and the outer tube 12 through a liquid pipe 26, the liquid passage 20 of a connection member 18, and a liquid feeding hole 14 of the inner tube 10, and the liquid pouring amount and the liquid pressure are detected. In such a way, the stress and the deformation property of a soft ground can be measured accurately.