PURPOSE: To make it possible to certainly and efficiently perform the strength test of a large structure receiving large load or large displacement by simple constitution.

CONSTITUTION: The titled apparatus is constituted so that one of a pair of test machines 12, 13 having the operation modes of both control systems of load control and displacement control is arranged to one side of a test body 11 and the other one of them is arranged in opposed relation to the other side of the test body 11. The test body 11 and the test machines 12, 13 are connected by a pair of load jigs 15, 17 and fixed to the surface of a floor 14. In testing the strength of the test body, one of the test machines is operated by the displacement control system and the other one of them is operated by the load control system to make it possible to apply load twice that of the test machine low in load capacity. By operating both test machines 12, 13 by the load control system, the sum load of the load capacities of the test machines 12, 13 can be applied to the test body 11. Further, by operating the test machines 12, 13 by the displacement control system, the summed displacement of the strokes of the test machines 12, 13 is applied to the test body 11.