In a biosensor for measuring a specific substance in a liquid sample, one or a combination of sugar alcohol, metallic salt, organic acid or organic acid salt which has at least one carboxyl group in a molecule, and organic acid or organic acid salt which has at least one carboxyl group and one amino group in a molecule, is included in a reagent layer provided on electrodes, thereby providing a highly-accurate biosensor which is excellent in stability and has high response (sensitivity, linearity) of the sensor to the substrate concentration.