A valve comprising: a valve housing (191, 192) that has a first ventilation hole, a second ventilation hole, and a third ventilation hole; and a valve body that configures a first region communicating with the first ventilation hole and a second region communicating with the second ventilation hole in the valve housing (191, 192), wherein the valve body has a fixed portion with a first through-hole communicating the first region and the second region with each other and a movable portion switching a communication state between the second ventilation hole and the third ventilation hole, the valve body is fixed to the valve housing such that: when a pressure in the first region is higher than a pressure in the second region, the valve body blocks communication between the second ventilation hole and the third ventilation hole and communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween, and when the pressure in the first region is equal to or lower than the pressure in the second region, the valve body communicates the second ventilation hole and the third ventilation hole with each other characterised in that when the pressure in the first region is equal to or lower than the pressure in the second region the valve body also communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween. a valve housing (191, 192) that has a first ventilation hole, a second ventilation hole, and a third ventilation hole; and a valve body that configures a first region communicating with the first ventilation hole and a second region communicating with the second ventilation hole in the valve housing (191, 192), wherein the valve body has a fixed portion with a first through-hole communicating the first region and the second region with each other and a movable portion switching a communication state between the second ventilation hole and the third ventilation hole, the valve body is fixed to the valve housing such that: when a pressure in the first region is higher than a pressure in the second region, the valve body blocks communication between the second ventilation hole and the third ventilation hole and communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween, and when the pressure in the first region is equal to or lower than the pressure in the second region, the valve body communicates the second ventilation hole and the third ventilation hole with each other characterised in that when the pressure in the first region is equal to or lower than the pressure in the second region the valve body also communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween. when a pressure in the first region is higher than a pressure in the second region, the valve body blocks communication between the second ventilation hole and the third ventilation hole and communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween, and when the pressure in the first region is equal to or lower than the pressure in the second region, the valve body communicates the second ventilation hole and the third ventilation hole with each other characterised in that when the pressure in the first region is equal to or lower than the pressure in the second region the valve body also communicates the first ventilation hole and the second ventilation hole with each other with the first through-hole interposed therebetween.