A valve includes a valve body, a diaphragm dividing the inside of the valve body into first and second valve chambers and being displaced under a pressure of fluid, first and second openings in communication with the first valve chamber, and a third opening in communication with the second valve chamber. When a pump is not driven, the force applied to a side of the diaphragm facing the second valve chamber is greater than the force applied to a side of the diaphragm facing the first valve chamber, and the second opening is sealed by the diaphragm. When the pump is driven and the force applied to the side of the diaphragm facing the first valve chamber becomes greater than the force applied to the side of the diaphragm facing the second valve chamber, the diaphragm allows the first and second openings and to communicate with each other.