A frequency characteristics measuring apparatus (10) is disposed in the vicinity of an end of refrigerant piping (70), the end of which is connected to an outdoor unit (50), that connects the outdoor unit (50) and an indoor unit (60) of an air conditioner, and measures frequency characteristics of the refrigerant piping (70). A filter (30) is attached at a position between the outdoor unit (50) and a position where a terminal (11) of the frequency characteristics measuring apparatus (10) is connected, so as to wrap the refrigerant piping (70). A piping length calculating apparatus (20) is connected to the frequency characteristics measuring apparatus (10) via an interface cable (40), and acquires, via the interface cable (40), frequency characteristics measured by means of the frequency characteristics measuring apparatus (10). The piping length calculating apparatus (20) extracts a lowest anti-resonant frequency from the acquired frequency characteristics, and calculates the length of the refrigerant piping (70) on the basis of the extracted lowest anti-resonant frequency.