To provide a pressure detector capable of securing a necessary measurement range while suppressing increase in the capacity of a gaseous phase part.SOLUTION: A pressure detector includes a case which can be connected to a flow passage of a liquid, and a film member M mounted in the case and for partitioning between a liquid phase part which can fill a liquid in the flow passage and a gaseous phase part which can fill a gas, and which can displace according to the pressure of the liquid filled in the liquid phase part, and the pressure detector detects the pressure of the liquid in the flow passage by detecting the pressure of the gaseous phase part. In the gaseous phase part, an opening Cb1 is formed which can allow a gas to flow in or flow out according to the displacement of the film member, and a flow passage R is formed which can hold the flowing-in or flowing-out of the gas by the opening in the process of the film member displacing to the gaseous phase part side.SELECTED DRAWING: Figure 9【課題】気相部の容量が増大してしまうのを抑制しつつ必要な測定レンジを確保することができる圧力検出器を提供する。【解決手段】液体の流路に接続可能なケースと、ケース内に取り付けられ、流路の液体を充填し得る液相部と、気体を充填し得る気相部とを区画するとともに、液相部に充填された液体の圧力に応じて変位可能な膜部材Ｍとを具備し、気相部の圧力を検出することにより流路における液体の圧力を検出する圧力検出器において、気相部は、膜部材の変位に応じて気体を流入又は流出させ得る開口Ｃｂ１が形成されるとともに、膜部材が気相部側に変位する過程で開口による気体の流入又は流出を保持し得る流通路Ｒが形成されたものである。【選択図】図９
