PURPOSE: To obtain a deinking agent containing a glycerol monofatty acid ester containing a specific fatty acid as an active component and capable of regenerating printed waste paper to regenerated paper having high whiteness in a high yield.

CONSTITUTION: Regenerated paper having high whiteness can be produced in a high yield by adding waste newspaper, magazine paper, printed paper, etc., to a treating liquid obtained by compounding (A) a glycerol monofatty acid ester composed of a 11-22C fatty acid and having excellent ink-peeling power with (B) a glycerol monofatty acid ester composed of a 8-14C fatty acid and having excellent frothing power at a weight ratio (A/B) of 2/98 to 98/2, further adding an anionic surfactant having frothing power, adding sodium hydroxide and hydrogen peroxide to the resaltant solution and subjecting the waste paper to defibration and flotation treatment, thereby sufficiently removing the ink having low frothing ratio and resistant to removing.