To provide a technique for determining whether a rigidity value can be calculated objectively, and also to provide a technique for calculating the rigidity value.

A rigidity value calculation apparatus comprises: an inputting means 12 for inputting information on a relation between a frequency and a phase in a vibration; a frequency-phase characteristic diagram creating means 22; a phase criterion setting means 23 for setting a phase criterion; a search range setting means 24 for setting a search range for searching a relationship between the phase and the phase criterion on a frequency-phase characteristic diagram; a search range moving means 25 for moving the search range; a phase comparing means 26 for comparing the phase with the phase criterion on the frequency-phase characteristic diagram; a determining means 27 for determining whether the rigidity value can be calculated, based on a comparison result from the phase comparing means 26; and a changing means 28 for changing a search zone or a reference phase.