Abstract: The biosensors of the present invention comprise an electrically insulating substrate, an electrically insulating cover connected to the substrate via a spacer layer, a reaction-detecting section formed on the substrate at a region sandwiched between the substrate and cover, and comprising at least one set of electrodes, and an external terminal to be connected to the reaction-detecting section, and a sealed sample-feeding path defined between the substrate and cover by the spacer layer, where the sample-feeding path has a portion intersecting the electrodes, as well as a cutting plane line provided at an outermost surface of the substrate or cover, which is a boundary between a sensor portion comprising electrodes and a sealed cap portion which does not comprise electrodes, and the cutting plane line is present at a position where, when the sealed cap portion is cut along the cutting plane line, the cut surface does not cross the electrodes and does cross the sample-feeding path, so that a sample-inlet port