A valve comprising: a first plate having a first vent hole; a second plate having a second vent hole; a channel forming portion joined to the first plate and the second plate and having an exhaust hole communicating with the outside; and a valve member positioned inside the channel forming portion, forming a first chamber with the first plate, and forming a second chamber with the second plate, wherein the channel forming portion includes a first channel connecting the first vent hole and the second vent hole and a second channel connecting the second vent hole and the exhaust hole, the valve member being configured to deform on the basis of a pressure of the first chamber and a pressure of the second chamber so as to connect the first channel and interrupt the second channel or so as to interrupt the first channel and connect the second channel, and an opening of the second vent hole and a first principal surface of the second plate are flush with each other, characterized in that: the channel forming portion further includes an exhaust channel forming plate that has a first principal surface and a second principal surface and that forms an exhaust channel opened in at least the first principal surface, and an intermediate plate joined to the first principal surface of the exhaust channel forming plate so as to cover an opened portion of the exhaust channel formed in the first principal surface of the exhaust channel forming plate, wherein at least a section of the exhaust channel protrudes from an outer edge of the intermediate plate; wherein the intermediate plate, the exhaust channel forming plate, and the second plate having the second vent hole are laminated in sequence to form the exhaust channel. a first plate having a first vent hole; a second plate having a second vent hole; a channel forming portion joined to the first plate and the second plate and having an exhaust hole communicating with the outside; and a valve member positioned inside the channel forming portion, forming a first chamber with the first plate, and forming a second chamber with the second plate, wherein the channel forming portion includes a first channel connecting the first vent hole and the second vent hole and a second channel connecting the second vent hole and the exhaust hole, the valve member being configured to deform on the basis of a pressure of the first chamber and a pressure of the second chamber so as to connect the first channel and interrupt the second channel or so as to interrupt the first channel and connect the second channel, and an opening of the second vent hole and a first principal surface of the second plate are flush with each other, characterized in that: the channel forming portion further includes an exhaust channel forming plate that has a first principal surface and a second principal surface and that forms an exhaust channel opened in at least the first principal surface, and an intermediate plate joined to the first principal surface of the exhaust channel forming plate so as to cover an opened portion of the exhaust channel formed in the first principal surface of the exhaust channel forming plate, wherein at least a section of the exhaust channel protrudes from an outer edge of the intermediate plate; wherein the intermediate plate, the exhaust channel forming plate, and the second plate having the second vent hole are laminated in sequence to form the exhaust channel.