This invention provides cationic acrylamide polymers which are highly effective as paper strength agents, drainage agents and suspension flocculants, and which do not show much temporal deterioration; it also provides a method of manufacturing said polymers wherein the manufacturing equipment is compact and can be installed on site, and the cationicity of the polymers can be modified in a short time.This invention comprises a method of manufacturing cationic acrylamide polymers by reaction, with a hypohalogenite, of a (meth)acrylamide homopolymer, a copolymer of (meth)acrylamide and acrylonitrile, a copolymer of (meth)acrylamide and N,N-dimethylacrylamide, in a high temperature range of 50.degree.-110.degree. C. for a short time; the polymers manufactured by said process; and paper strength agents, drainage agents and flocculants having these polymers as their principal constituent.