FLOW CHANNEL OPENING AND CLOSING DEVICE

PROBLEM TO BE SOLVED: To provide a flow channel opening and closing device capable of securing an instantaneous flow rate sufficient for washing a toilet bowl even when feed-water pressure is low.SOLUTION: A flow channel opening and closing device comprises: a main valve provided with a main valve body and a main valve seat which open and close a flow channel between a primary flow channel and a secondary flow channel; and a constant flow valve provided with a constant flow valve body and a constant flow valve seat which maintain a constant instantaneous flow rate of water flowing from the primary flow channel to the secondary flow channel. The main valve and the constant flow valve are integrated as a valve body member. The flow channel opening and closing device also has: a back pressure chamber which allows back pressure to move the main valve body close to the main valve seat; a position adjustment member which moves along a sliding direction of the valve body member in a manner that adjusts a drive amount of the valve body member; a sub-back pressure chamber which is installed at an opposite side to the back pressure chamber with the position adjustment member placed in between and allows the back pressure to move the position adjustment member close to the valve body member; and a flow channel adjustment mechanism which is installed in the middle of a sub-primary flow channel communicating the primary flow channel with the sub-back pressure chamber and can adjust a cross-sectional area of the sub-primary flow channel.