the present invention provides a catalyst , which has enough catalytic activity as a transition metal particle catalyst including platinum family and the like , is easily separable from products , is reusable and is easily prepared . to prepare the transition metal cluster catalyst of the present invention , an insoluble complex is prepared by forming a complex between a polymer with nitrogen - containing group , such as pyridinium and ammonium group in the principal chain , and a later transition metal compound ; and then reducing the complex with a reductant . the transition metal forms clusters , which are stabilized by the polymers . namely , the present invention is a transition metal cluster catalyst , wherein transition metal clusters are supported by a polymer , which is obtained by reduction reaction of a complex of a transition metal and a polymer with nitrogen - containing group . the transition metal cluster catalyst of the present invention is an extremely useful catalyst for oxidation , reduction , cross - coupling , heck reaction , alkylation reaction and the like .