sic may also be used fig4 is a sectional diagram showing a main portion of a fourth embodiment i e a seal diaphragm with film in fig4 a ceramic film 1 and a hydrogen diffusion blocking film 3 are coated in two layers on the left surface of the seal diaphragm 10 i e the surface on the fluid side here the ceramic film 1 is the same as in the first embodiment the hydrogen diffusion blocking film 3 is made of a material into which hydrogen is hard to diffuse or into which hydrogen does not diffuse such as gold or tungsten in the fourth embodiment the ceramic film 1 coated on the uppermost surface hardly allows the electrons to be delivered from the seal diaphragm 10 to the hydrogen ion thus making it difficult for the hydrogen atoms to adhere to or pass through the seal diaphragm the hydrogen diffusion blocking film 3 encourages blocking of the hydrogen atoms from adhering to or passing through the seal diaphragm 10 fig5 is a sectional view common to the respective embodiments in fig5 each of the above mentioned seal diaphragms with film 41 42 43 44 is provided as a seal diaphragm and tetrafluoroethylene resin as a corrosion resistant resin is coated on the inner surfaces of a cover 19 and a connecting.