A biosensor for quantifying a specific compound has a reaction layer containing at least an enzyme, and an electrode system having a working electrode and a counter electrode formed on an insulating base plate; the biosensor detects the specific compound contained in a sample on the basis of an electrochemical response. In quantifying, the working electrode and the counter electrode are short-circuited before the voltage is applied therebetween. The short-circuiting eliminates measuring errors that may occur due to nonuniform dissolution of the reaction layer in a sample, and achieves highly reliable quantification of a specific compound.