To provide an aqueous primer capable of exhibiting excellent adhering strength by applying on the surface of an adherend on adhering the adherend such as an organic material and a porous organic material, etc.

This aqueous primer characterized by containing a polychloroprene and an EVA resin as essential components is applied on the surface of the adherend in advance before applying an adhesive to obtain a high adhering strength. The EVA resin is an ethylene-vinyl acetate copolymer resin, and is preferably used in an emulsion state. It is preferable to contain ≥40% mass ratio of ethylene in the EVA resin for improving the adhering strength of the adherend, and further more preferable to contain ≥60%.