An in-plane compressive strength evaluation device that is disposed in a steam generator and evaluates an in-plane compressive strength of a tube support plate, in which are formed a number of through-holes through which heat transfer tubes pass, the in-plane compressive strength evaluation device comprising: a memory unit in which, when a test piece having substantially a same structure as the tube support plate that is actually used is formed and an in-plane compressive strength evaluation is performed by exerting a load in a state where the heat transfer tubes having a prescribed length are inserted into the through-holes formed in the test piece, respectively, an evaluation result related to the load and a displacement of the test piece is stored as first information; a first analysis unit that obtains, by producing a structural model of the test piece and by performing a simulation of the in-plane compressive strength evaluation under same conditions as the in-plane compressive strength evaluation, second information that is an evaluation result related to the load and the displacement in the structural model; an adjustment unit that adjusts an elemental factor of the structural model that influences the in-plane compressive strength such that the second information that is obtained by the first analysis unit approaches the first information that is stored in the memory unit; and a second analysis unit that, in a state where the elemental factor that is used when the second information approaches the first information most closely, or when a difference between the second information and the first information falls within an allowable range is maintained, expands the structural model into a structural form of the tube support plate that is actually applied to the steam generator and performs the in-plane compressive strength evaluation using the expanded structural model. a memory unit in which, when a test piece having substantially a same structure as the tube support plate that is actually used is formed and an in-plane compressive strength evaluation is performed by exerting a load in a state where the heat transfer tubes having a prescribed length are inserted into the through-holes formed in the test piece, respectively, an evaluation result related to the load and a displacement of the test piece is stored as first information; a first analysis unit that obtains, by producing a structural model of the test piece and by performing a simulation of the in-plane compressive strength evaluation under same conditions as the in-plane compressive strength evaluation, second information that is an evaluation result related to the load and the displacement in the structural model; an adjustment unit that adjusts an elemental factor of the structural model that influences the in-plane compressive strength such that the second information that is obtained by the first analysis unit approaches the first information that is stored in the memory unit; and a second analysis unit that, in a state where the elemental factor that is used when the second information approaches the first information most closely, or when a difference between the second information and the first information falls within an allowable range is maintained, expands the structural model into a structural form of the tube support plate that is actually applied to the steam generator and performs the in-plane compressive strength evaluation using the expanded structural model.