an electrofusion joint used as a pipe joint for plastic pipes , wherein a coil electric heating wire is embedded inside and it is heated by application of an electric current after insertion of the plastic pipes to cause fusion / adhesion at the contact surface therebetween . the characteristic feature is to use one or more means of items to below to improve adhesion of the coil and the resin constituting the joint : to use adhesive resins for the resin constituting the joint . to provide a coil with the surface substantially not oxidized . to cover the surface of the coil with a substance which has an affinity to both the resin and the coil .