A behavior inspection apparatus includes: a first measurement tool group including a set of first measurement tools each of which measures a first distance change amount that is a change amount of a distance between a first pipe position in the first pipe and a first reference position of a sleeve of the extensible flexible pipe joint; and a second measurement tool group including a set of second measurement tools each of which measures a second distance change amount that is a change amount of a distance between a second pipe poison in the second pipe and a second reference position of the sleeve. The first and second measurement tools are arranged at different positions in a circumferential direction of the sleeve. Displacement positions of the first and second pipes with respect to the joint are computed based on the measurement data by the first and second measurement tool groups.