To provide an insulated corrosion-proof joint in a convenient and inexpensive structure of preventing rusting due to the potential difference between a steel pipe, arranged in a water channel piping system and a joint having different material.

An insulating layer 11 and a sealing layer 12 are laid on a threaded area between the bronze joint 1 and the steel pipe, for example. These two layers provide electrically complete insulation between the joint 1 and the steel pipe 2. Therefore, the rusting of the steel pipe 2 is prevented. The insulating layer 11 and the seal layer 12 are easily applied on the joint 1 or the steel pipe 2 with coating treatment, resulting in relatively convenient and inexpensive work.