To provide a pressure-sensitive adhesive effectively maintaining high adhesive characteristics which the pressure-sensitive adhesive inherently has at an initial stage in application thereof, and exhibiting strong adhesive strength to an adherend after the application.

This pressure-sensitive adhesive modified with the surface-reactive functional groups is given by coating a surface of the pressure-sensitive adhesive with an amino group-containing polymer (A) through interfacial contact reaction, so that the surface of the pressure-sensitive adhesive is modified with amino groups, wherein the polymer (A) is given by substituting hydrogen atoms of at least a part of the amino groups in its molecule with organic groups each composed of five or more atoms. Adhesive strength of the pressure-sensitive adhesive to the specified adherend may be increased with time, after the application. A hydrocarbon residue which may have a substituent is preferably used as the organic group for substituting the amino group in the amino group-containing polymer (A). The amino group- containing polymer (A) is prepared by reacting the amino groups in (b) a polymer having the amino groups with amino group-reacting functional groups in (c) compounds containing the amino group-reacting functional group.