There is provided a biosensor for measuring a measuring target substance in a sample comprising an insulating substrate, an electrode pair provided on the insulating substrate, and a reagent that includes an oxidoreductase and an electron transfer substance and is provided at least on a working electrode of the electrode pair, wherein the working electrode is composed of one or more kinds of nickel alloys selected from the group consisting of a nickel-ruthenium alloy, a nickel-tungsten alloy, and a nickel-vanadium alloy.