PURPOSE: To make the measurement of stress accurate, by making it possible to move loading plates in the same direction as a loading rods in the Z direction, associating the movement of the loading plates in the Z direction with the movement of the load mounting rods, thereby preventing the effect on the measured data due to the side friction.

CONSTITUTION: A pair of side plates 52 of a movable body 5 has a larger interval than the size of a body under test 1, and the plates face each other. On the inner surface of the side plates, hydraulic jacks 31 and loading plates, which are connected to output shafts 32 of the hydraulic jacks 31, are provided. Loading plates, which are fixed in association with the movable frame body 5 are provided. The loading plates face each other so as to hold the body under test 1. A load cell for measuring the load is arranged on one loading plate. In this way, the sum of the frictional forces at contact surfaces of the movable plates and the body under test becomes zero. The frictional force itself which acts on the part between the body under test and the loading plates is reduced. The effect on the measured data due to the side friction is prevented, and the measurement becomes accurate.