An in-plane compressive strength evaluation device (10) provided with a memory unit (21) into which, when an in-plane compressive strength evaluation is actually performed using a test piece, an evaluation result is stored as first information; a first analysis unit (22) that obtains second information that is an evaluation result related to the load and a displacement of the structural model; an adjustment unit (23) that adjusts an elemental factor of the structural model that influences the in-plane compressive strength such that the second information approaches the first information; and a second analysis unit (24) that, in a state where the elemental factor used when the second information approaches the first information most closely expands the structural model into the structural form of the actual tube support plate, and that performs the in-plane compressive strength evaluation using the expanded structural model.