To provide a flocculant responding to the need of users to perform a treatment by a combination of non-acrylamide polymers, particularly, a user having the need in treatment of a wide variety of sludge types including digestive sludge which is generally treated with a high-molecular-weight sludge dehydrating agent.

A sludge dehydrating agent is composed of non-acrylamide polymers of an amidine cationic polymer: 40-75 mass%; a vinylamine cationic polymer: 12.5-30 mass%; a dialkylaminoethyl (meth)acrylate methyl chloride quaternary salt homopolymer: 12.5-30 mass%; and a dialkylaminoethyl (meth)acrylate homopolymer: 0-25 mass% (the total of all the components being 100 mass%).