A method for quantifying a target substance, comprising: bringing a sample containing the target substance into contact with a biosensor which comprises an enzyme electrode containing an oxidoreductase and a counter electrode; measuring a change in the potential difference between the enzyme electrode and the counter electrode due to oxidation reaction of the target substance catalyzed by the oxidoreductase; and calculating the concentration of the target substance based on the change in the potential difference; wherein a potential is applied between the enzyme electrode and the counter electrode before the measurement of the change in the potential difference.