A sensor including a sensor element including a plurality of electrode terminals, terminal metal fittings, a terminal surrounding member, and lead wires connected to respective terminal metal fittings. The terminal surrounding member is divided into a front side surrounding member and a rear side surrounding member in the front-rear direction, and a rear end face of the front side surrounding member abuts a front end face of the rear side surrounding member. At least one of the terminal metal fittings includes a protruding piece portion protruding in a lateral direction and held between the rear end face of the front side surrounding member and the front end face of the rear side surrounding member.