To prevent sewage from remaining in a suction pipe when sewage is not sucked and prevent adhesion of suspensions by providing a vent hole provided in a pipe wall near a vacuum valve and a vacuum auxiliary valve that opens and closes the vent hole in the suction pipe that sucks sewage in a water storage tank and specifying opening and closing actions of the vacuum valve and the vacuum auxiliary valve.

A vacuum valve unit U is comprised of a water storage tank 1, an inflow pipe 2, a connection pipe 3, a suction pipe 4, a vacuum valve 5, a vacuum auxiliary valve 8 that opens and closes a vent hole provided in a pipe wall near the vacuum valve 5 of the suction pipe 4 and a water level sensor 9. When the vacuum valve 5 closes the joint between the suction pipe 4 and the connection pipe 3, the vacuum auxiliary valve 8 opens the vent hole provided in the wall of the suction pipe 4, keeps the interior of the suction pipe 4 at an atmospheric pressure and drops sewage in the suction pipe 4. When the water level sensor 9 detects that the level of sewage has reached a prescribed height and the vacuum valve 5 opens the joint between the suction pipe 4 and the connection pipe 3, the vacuum auxiliary valve 8 closes the vent hole of the suction pipe 4 and sucks sewage in the water storage tank 1 without trouble.