PURPOSE: To facilitate operation and to improve working efficiency by passing ice grains or liquid contg. the ice grains into a pipe and cleaning the pipe by utilizing a vacuum suction system or pressurization system or the like.

CONSTITUTION: In the case of cleaning by using the vacuum suction system, a suction device 2 is connected to the end of a suction hose 4 connected to the large-diameter side of the piping 1 to be washed within a building to maintain the inside of the pipe at a vacuum. Next, the ice grains or the liquid 3 contg. the ice grains is sucked through a flexible hose 5 from the one small- diameter side into the pipe where the liquid is passed. At this time, the water contg. the ice grains is first sucked and thereafter, the ice grains are mainly sucked and the inside of the pipe is successively washed from the small-diameter side toward the large-diameter side. Even the intricate piping systems and even the piping of any diameters are thus efficiently washed without clogging.