To limit a contact area for grounding, to prevent high heat by ensuring contact/connection of grounding and securing conductivity, to prevent discoloration of surrounding coating, and to allow simple and stable installation at an arbitrary position.

This connecting device is constituted of a base body A consisting of a nonconductive member in which an upper and lower plates 2, 3 each with a grounding inserting hole drilled in the center on the same center line are combined with plural columnar parts 4 that are surrounding the grounding inserting hole and that are each provided with a supporting leg inserting hole penetrated in the same direction as the center line; is constituted of a supporting leg B for fixing tack welding consisting of a conductive member which is freely rotatably inserted and supported in the supporting leg inserting hole of each columnar part, which is provided with a tip end projecting from the lower plate, and which is equipped with a rotary means at the rear end; and is constituted of a grounding assembly in which a conductive electrode-loading body 14 is connected to a grounding body 8 that is equipped with a spring pressing in the grounding face direction, that is supported vertically movably and freely rotatably in the grounding inserting hole of the base body, and that has a tip end projecting from the supporting leg for fixing tack welding.