Abstract: In a biosensor for measuring glucose in a liquid sample, an additive agent which is one of an organic acid or organic acid salt having at least one carboxyl group in a molecule, an organic acid or organic acid salt having at least one amino group or carbonyl group in a molecule, a sugar alcohol, and a solubilized protein, or a combination thereof is added into a reagent layer including glucose dehydrogenase having flavin adenine dinucleotide as a coenzyme, which is provided on an insulating substrate. Thereby, the substrate specificity to glucose and the preservation stability can be enhanced, and further, reactions to sugars other than glucose can be avoided.