Provided is a material that, when compared with SAPd, exhibits the similar activity in cross-coupling (CC) reactions, can decrease the amount of catalytic metal that is mixed into the reaction product, and increases the number of times use can be repeated. Provided are a catalyst and a catalyst precursor that use a catalytic metal other than Pd and that exhibit the CC reaction activity similar to when Pd is used. Provided are a catalyst and a catalyst precursor that exhibit the similar CC reaction activity when using Pd or a catalytic metal other than Pd, without using a carrier such as metal and without using piranha solution. A composite wherein catalytic metal nanoparticles are dispersed in a continuous phase comprising a polymer having C2-6 alkylene group units and phenylene group units (an alkylene group unit being bonded to at least the first and fourth position of the phenylene group unit). The particle diameter of the catalytic metal nanoparticles is at most 20nm. A composite structure including a substrate, and the aforementioned composite provided to the surface of the substrate. A method for manufacturing the composite structure by dehydrocondensating, in the presence of a catalytic metal compound, a benzene compound having at least two alkyl groups (two of the alkyl groups being at the first and fourth position) in order to form the composite on the substrate surface.