To provide a high polymer coagulant superior in the dehydration ratio in a dehydration process of organic sludge and concentration efficiency in a concentration process before this dehydration process, even in a little addition amount (the addition ratio).

The present invention uses the cation high polymer coagulant including a cation high polymer (A) having salt viscosity of 130-210 mPa s and a cation high polymer (B) having salt viscosity of 5-60 mPa s. The cation high polymer (A) has a colloid equivalent value (CEa) of 1.2-4.8 meq./g, and the cation high polymer (B) has a colloid equivalent value (CEb) of 1.7-4.9 meq./g, and the ratio (CEb/CEa) of these colloid equivalent values is desirably 0.5-2. Low molecular ammonium salt (T) is further desirably included.