PROBLEM TO BE SOLVED: To significantly reduce or avoid the error due to electrical coupling between a measured medium and an electrode, in a surface acoustic wave sensor where measurement and monitoring of the conductivity, relative permittivity, viscosity, and the like, of a desired medium are achieved based on the propagation characteristics of surface acoustic wave on a piezoelectric substrate.SOLUTION: A surface acoustic wave sensor has a plurality of sealing members formed on a piezoelectric substrate, and individually sealing a plurality of electrodes performing energy conversion of an electric signal and a surface acoustic wave. The surface acoustic wave sensor detects the presence or absence or the characteristics of a medium in a reaction field, as the propagation characteristics of the surface acoustic wave in the reaction field surrounded by the plurality of electrodes on the piezoelectric substrate. A plurality of covering members are attached individually to the whole area at the top of the plura
