A frequency characteristics measurer is disposed in the vicinity of an end of refrigerant piping, the end of which is connected to an outdoor unit, that connects the outdoor unit and an indoor unit of an air conditioner, and measures frequency characteristics of the refrigerant piping. A filter is attached at a position between the outdoor unit and a position where a terminal of the frequency characteristics measurer is connected, so as to wrap the refrigerant piping. A piping length calculator is connected to the frequency characteristics measurer via an interface cable, and acquires, via the interface cable, frequency characteristics measured by means of the frequency characteristics measurer. The piping length calculator extracts a lowest anti-resonant frequency from the acquired frequency characteristics, and calculates the length of the refrigerant piping on the basis of the extracted lowest anti-resonant frequency.