PURPOSE: To detect accurate stress by sealing a pressure converter and a liquid with constant compressibility in a casing and by absorbing a liquid, as much as the volume of the compression of the casing due to external force, with the compressibility of the liquid and the strain of the pressure converter.

CONSTITUTION: In pressure receiving casing 7 that getting strained equally by external equal force operating in every direction and made of surfaces of point symmetry, pressure converter 9 and liquid 8 with constant compressibility are sealed. As pressure 6 in the earth operates on pressure receiving casing 7 and casing 7 contracts, liquid 8 is pushed away according to the extent of the contraction and while its volume is absorbed with the compressiblity of liquid 8 and the strain of pressure converter 9, the detection value of converter 9 is passed through amplifier 13 and displayed on display part 14. Therefore, the pressure in the earth never causes the pressure receiving surface to expand and strains in the earth in respective three orthogonal axial directions are ignored, so that the precision of the detection can be improved.