To restrain a lowering of a signal value which is output from a biosensor and to shorten the time required for the coating process of a solution by a method wherein the solution which contains a physiologically active substance and a hydrophilic polymer substance is coated so as to cover an electrode on a substrate, the solution is dried and a coating film is formed.

A solution which contains a physiologically active substance and a hydrophilic polymer substance is prepared. The solution is coated so as to cover a substance electrode which is formed on an insulating substrate, it is dried, and a coating film is formed. When, e.g. glucose oxidase(GOD) is adopted as physiologically active substance, the solution contains the GOD together with phosphate and the hydrophilic polymer substance (sodium alginate, polyvinyl alcohol, polyvinyl pyrrolidone or the like). At this time, when two kinds of solutions are mixed, a method by a reversing mixing operation, a mixer, a stirrer or the like is applied. In addition, the substrate electrode which is coated with the solution is a working electrode, and it is preferable that the solution is dried in an environment whose humidity is about 10 to 20%.