There is an essential limitation that only surface principal stress sum variation (.DELTA.(.sigma..sub.1+.sigma..sub.2)) can be measured as physical quantity by a thermoelastic stress measurement technique, and furthermore respective principal stress components are unknown, and pure shearing stress acting on an object cannot be measured because it causes no temperature variation. Thus, in the present invention, when stress state of the object is measured, not only the thermoelastic stress measurement but also stress measurement (mechanoluminescence measurement) using a mechanoluminescence material is used in combination. Consequently, stress can be measured in detail; for example, principal stress component values (.sigma..sub.1 and .rho..sub.2) can be known while exceeding the principle limitation of the thermoelastic stress measurement technique.