A structure evaluation system comprising: a plurality of sensors (10-1,...,10-n) configured to detect elastic waves generated from a structure; a position locator configured to derive a wave source distribution of the elastic waves generated from the structure, on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors; a velocity calculator configured to derive a propagation velocity distribution indicating a distribution of the propagation velocity of the elastic waves generated from the structure, by using tomography analysis on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors; and an evaluator configured to: segment the wave source distribution into two regions including a source-sparse region in which the wave sources are sparsely arranged based on a first reference value and a source-dense region in which the wave sources are densely arranged, and a predetermined range including said first reference value; segment the propagation velocity distribution into two regions including a fast region in which the propagation velocity is high based on a second reference value and a slow region in which the propagation velocity is low, and a predetermined range including said second reference value, superimpose the segmented wave source distribution and the segmented propagation velocity distribution; evaluate each region of the structure as belonging to one of the four phases resulting from superimposing said two regions of the segmented wave source distribution and said two regions of the segmented propagation velocity distribution, or not belonging to any of said four phases; derive an evaluation result distribution indicating to which phase each of the regions of the structures corresponds; and output the derived evaluation result distribution. a plurality of sensors (10-1,...,10-n) configured to detect elastic waves generated from a structure; a position locator configured to derive a wave source distribution of the elastic waves generated from the structure, on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors; a velocity calculator configured to derive a propagation velocity distribution indicating a distribution of the propagation velocity of the elastic waves generated from the structure, by using tomography analysis on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors; and an evaluator configured to: segment the wave source distribution into two regions including a source-sparse region in which the wave sources are sparsely arranged based on a first reference value and a source-dense region in which the wave sources are densely arranged, and a predetermined range including said first reference value; segment the propagation velocity distribution into two regions including a fast region in which the propagation velocity is high based on a second reference value and a slow region in which the propagation velocity is low, and a predetermined range including said second reference value, superimpose the segmented wave source distribution and the segmented propagation velocity distribution; evaluate each region of the structure as belonging to one of the four phases resulting from superimposing said two regions of the segmented wave source distribution and said two regions of the segmented propagation velocity distribution, or not belonging to any of said four phases; derive an evaluation result distribution indicating to which phase each of the regions of the structures corresponds; and output the derived evaluation result distribution.