PURPOSE: To facilitate and quicken operation of attaching/detaching a contact point member and to simplify and secure operation of positioning the contact point member by forming a horizontal part of the contact point member of an elastic substance.

CONSTITUTION: Contact point supporting parts 62a, 62b are integrally formed on both lower sides of a cylindrical body 61, and in the supporting part 62a, side walls 63a-63c are formed into a nearly U-shape and a bottom wall 63d is formed. The bottom wall 63d is provided with a notch 63e while the supporting part 62b is similarly provided with side walls 64a-64d and a notch 63e of a bottom wall 64d. A contact point member 65 is constituted of insulative rubber having a horizontal part 65a and swelling parts 65b, 65c, and conductive rubber having contact point parts 65d, 65e. Both end parts of the horizontal part 65a are retained to extend the member 65 in the horizontal direction to pass the horizontal part 65a through notches 63e, 64e. Tensile force is released in a state where the horizontal part 65a and the swelled parts 65b, 65c are positioned above the bottom walls 63d, 64d. Accordingly, the member 65 is contracted, and supported by supporting parts 62a, 62b to be positioned.