PURPOSE: To evaluate the induced maximum stress and remaining stress by forming a measurement face at the minimum gap to the inner face of extruding or molding dies as to make the measurement face movable freely in rectangular three directions and measuring shear strength and compression force at the time of solidification or extrusion by a sensor squeezed into molding dies.

CONSTITUTION: A measuring apparatus 4 is so installed at a gap from the wall of plastic extrusion-molding dies composed of an upper die 1, a lower die 2, and a molded body 3 of molding dies as to conform the surface 9 to the product face. A sensor head 5 is guided in the sensor sleeve 6 while being kept at a gap S to the sleeve and supported by a sensor 7. The sensor 7 is fastened in the lower die 2 of screw threads. The gap S is kept in minimum so as to make the measuring face freely movable in three directions at right angles and not to pass a liquid or viscous material through the gap S. The sensor 7 is provided with a pair of crystals with the same polarity and detects the vertical pressure P2, shearing force δx and converts into electric signals, and thereby the maximum stress and the residual stress are evaluated by a differentiator and adder unit.