To provide a pressure-sensitive adhesivity imparting agent capable of imparting adhesivity such as excellent adhesive power and constant-load retainability to an aqueous pressure-sensitive adhesive agent, and capable of not causing a decrease in adhesive power due to influences of moisture and wet heat and imparting excellent adhesion excellent in wet heat resistance; and to provide a composition for an aqueous pressure-sensitive adhesive agent and an aqueous pressure-sensitive adhesive agent containing the same.

A pressure-sensitive adhesive agent contains a vinyl polymer (A) having a weight-average molecular weight in the range of 500 to 30,000 obtained by polymerizing a monomer (a) having a polymerizable surfactant (a1) and a vinyl monomer (a2) having a nitrogen atom as essential components.