An assessing device capable of assessing presence or absence of local damage in a structure is provided. The assessing device includes a dominant frequency identifying unit that identifies a dominant frequency of a vibration at each of a plurality of spots in a structure, based on information indicating the vibration at each of the plurality of spots, a phase difference identifying unit that identifies a phase difference at the dominant frequency between the vibrations at the plurality of spots, based on the dominant frequency and information indicating the vibrations; and an assessing unit that assesses damage in the structure, based on the phase difference.