To obtain a decolorizer composition capable of perfectly erasing dye images drawn with an ink comprising a leuco dye, etc. on a support such as a white board by adding a polymer base having specific repeating constituting units.

This decolorizer composition contains a polymer base having repeating constituting units containing nitrogen atoms, preferably a polymer comprising constituting units of the formula [A is a repeating constituting unit; B is a repeating constituting unit; R1 is H or a lower alkyl; Q is a single bond, an alkylene, phenylene or the like; R2 to R4 are each H, an alkyl, an aryl or the like; X is an anion; (X), (y) and (z) are each the mol percent of each minimum constituting unit constituting the constituting unit of the formula; (x) is 0-100; (y) is 0-90; (z) is 0-90; (x)+(y)+(z)=100].