PURPOSE: To prevent a hydrophilic film from being clogged and to enable the hydrophilic film to be used for a long period by bringing sample liquid into contact with one surface of the hydrophilic film and carrier liquid into contact with the other surface.

CONSTITUTION: When the carrier liquid is sent from an intake pipe 3 to an enzyme electrode 16 by pressure, it is discharged from an outlet pipe 4 through the pipe 3, the longitudinal hole 12 of a sampling part 1, a flow passage 8 contacting the hydrophilic film 9, a mixer 13, the longitudinal hole 21 of an electrode cell 2, a measurement chamber 22, and the lateral hole 23 of the cell 2. The carrier liquid is fed and stopped periodically and repeatedly through this path, a specific material in the sample liquid which penetrates the film 9 during stop periods is diffused in the carrier liquid, mixed in the mixing chamber 13 during pressure feed periods, and sent to the measurement chamber 22. At the same time, part of the carrier liquid is formed out of the film 9 to the sample liquid side to back-wash the film 9, which is therefore prevented from being clogged and usable for a long period.