The present invention provides a biosensor that can be used for easy and quick quantitative analysis of a specific component in a sample with high precision and a method for manufacturing such a biosensor. The present invention also provides a biosensor that can be used for a highly precise quantitative analysis after an extended period of storage, specifically, a biosensor with excellent storage stability, and a method for manufacturing such a biosensor. The present invention relates to a biosensor comprising an electrically insulating substrate (1); an electrode (2) having a working electrode (21) and a counter electrode (22) formed on the substrate; and a reaction part (4) that is adhered to one end of the electrode (2); the reaction part (4) being mainly composed of a hydrophilic polymer comprising an oxidoreductase, an electron acceptor, fine crystalline cellulose powder, and hydrophilic and hydrophobic segments.