Existing fishing port facilities form a huge stock for which deterioration diagnosis and repair construction have started throughout Japan. Hence a simple and precise method for the deterioration diagnosis is needed. This study aimed to develop a simple deterioration diagnosis method applicable to fishing port facilities, and a proposed method using impact-echo was extensively tested through the inspection of existing structures. The results provided a quantitative measure of the immediacy of countermeasures and a simple deterioration diagnosis method for proper selection of detailed inspection. Availability of the proposed method was confirmed through tests at existing fishing port facilities.