A detection section (a sensor substrate according to the invention) is used in such a manner that it is inserted into a living body by being guided by a needle section (insertion needle) to be stuck and inserted into the living body. The detection section includes a first region which is provided in a tip end portion of the detection section and includes an electrode layer (detection electrode), a third region which includes a wiring section and has a smaller width than the width of a slit of the needle section (insertion needle), and a second region which is provided between the first region and the third region and has the same width as the width of the third region by gradually decreasing from the width of the first region.
