To dispense with attachment/detachment work of a detection device to check for any damages in the piping keeping the detection device connected to the piping in a case of the inspection for a long time, and visually detect presence/absence of small damages in the piping.

A gas bag 1 having a gas injection valve 2 and comprising an air-tight film is communicated in an air-tight manner with one end part of a pipe 5 or a piping network to be inspected, and the other end part of the pipe 5 or the piping network is sealed by a plug body 6. Gas is filled in the gas injection valve 2 to fill the gas in the gas bag 1 and the pipe 5 or the piping network with gas, the gas bag is swollen, and any possible damages of the pipe 5 or the piping network are detected by whether the gas bag 1 is deflated or not.