The purpose of the present invention is to provide an adhesive composition leading to sufficient adhesive strength when used for bonding to a polyolefin resin molded article that bonds poorly with other members. Another purpose of the present invention is to provide an adhesive composition having excellent heat resistance (heat resistant adhesion) in the bonded part of a composite body obtained by joining a polyolefin resin-formed body and other member. This adhesive composition contains an organic solvent, a carboxyl group-containing polyolefin resin which is dissolved in this organic solvent and which has a melt flow rate of 5 to 40 g/10 min when measured at 130° C., and a polyfunctional isocyanate compound. This adhesive composition may further contain a carboxyl group-containing polyolefin resin having a melting point of 120° C. to 170° C.