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