A technique is provided, wherein any influence, which would be otherwise exerted on a reaction of an objective substance caused by a reagent enzyme by an interfering substance contained in a specimen, is suppressed in relation to an electrochemical sensor for measuring the objective substance contained in the specimen. A sensor comprises a substrate; a detecting unit which is provided on the substrate and which detects an objective substance; a filter which covers the detecting unit, which permits permeation of the objective substance on one hand, and which regulates permeation of an interfering substance contained in a sample on the other hand; and removing means which removes the interfering substance adhered to the filter.