To obtain a deinking agent excellent in surface tension reducing capability, permeability and having high deinking property due to stable foaming by using a specific polyglyceryl fatty acid ester.

A deinking agent comprising a polyglyceryl fatty acid ester expressed by formula (R is H or an alkyl; and (n) is an integer of 2-20), for example the polyglyceryl fatty acid esters obtained by using hexanoic acid, octanoic acid, 2-ethylhexanoic acid, (iso)nonanoic acid, decanoic acid, lauric acid, palmitic acid, stearic acid, oleic acid, etc., as raw fatty acids is prepared. Deinking treatment is carried out by adding 0.05-0.5 wt.% based on raw material wastepaper of the deinking agent only to a pulper process or both of the pulper process and the next retention-tower process or both of the pulper process and a floatator process, etc.