To determine the position of a deterioration area in a reinforced concrete structure utilizing an electromagnetic wave signal.

One or a plurality of computer readable data signal, i.e., a computer readable data signal in which respective signals represent an electromagnetic wave signal detected from an area of a concrete structure are received. One or a plurality of detection electromagnetic wave signals include an electromagnetic wave energy reflected from the concrete structure which is obtained as a result by that the electromagnetic wave signal is transmitted into the concrete structure. A deterioration degree of one or a plurality of areas in a substantial concrete structure is judged from one or a plurality of computer readable data signals.