To establish a pipe measuring and analyzing method to measure and analyze the maximum bending stress (or the total strain equivalent to it) in the elastoplastic region of a circular pipe on the basis of the sonic elasticity method.

The stress-strain adaptive function F(0x) of a material gradient αof the linear relation between the apparent complex refraction amount and plastic strain, and the acousto-elastic constant CA are previously determined, along with previous determination of the change equation of the apparent complex refraction amount Bt in the circumferential direction using the max. total strain as parameter in a circular pipe 1 receiving a bending try, and separately therefrom, the change information of the apparent complex refraction amount Bt in the circumferential direction of the pipe to be measured is measured, and the result from measuring is referred to the change equation, and also determination is made for the adaptive relationship between them, max. total strain E0x, and max. bending stress.