The cover body is an elastic member integrally formed of the upper side, the lower side, and the lateral side. The upper side preferably includes a display viewable window at a first end, and the lateral side preferably includes a sensor insertion opening at a second end opposite the first end with the display being viewable window on the upper side. The sensor insertion opening preferably includes a tubular protuberance configured to cover an outer circumference of the sensor insertion opening and protrudes outwardly from the sensor insertion opening.