To provide an adhesive usable at a surrounding temperature.

This adhesive for binding two cross-linked rubber compositions together and usable at the surrounding temperature contains a copolymer containing a urea or urethane group as a base. The copolymer is characterized in that the copolymer contains an isocyanate group, and is a reaction product of (1) a tri- or more-functional polyisocyanate containing an isocyanurate ring, (2) a functional polymer having amine groups or alcohol groups at both of two chain terminals, and belonging to the group consisting of a polyether diamine, a polyether diol, a polyester diol and an (ether-ester) diol copolymer, and (3) at least one trimerization catalyst for forming the isocyanurate ring from the isocyanate group, regulated so that the ratio of the total mols of the isocyanate groups to the total mols of the amine groups may be 1.5-2.2.