PURPOSE: To have easy replacement of valve seat by mounting a valve seat, which has a smaller dia. than a spacer insert hole provided in a top lid, at the bottom surface of a valve chest with possibility of removal.

CONSTITUTION: A plurality of outlets 13 are bored in the bottom surface of a valve chest 2 on one circumference, and a removable valve seat 15 is installed at each of these outlets 13. The outside dia. D2 of each valve seat is smaller than the outside dia. D1 of a spacer insert hole bored in a tap lid 2. Treatment liquid from each processing device is introduced to an inlet hole 10 of a pipeline switching device via each flow-in pipe 11. This makes it possible to remove a valve drive mechanism 7 and a spacer 6 and take out the valve seat 15 from the spacer insert hole, and repair can be done simply without requiring removal and movement of the valve bos 2.