To provide a one-pack type coating agent which excels in adhesion to a plastic base material and a topcoat and metallic pigment dispersibility and excels in water resistance and moisture resistance as well, its manufacturing method, and a coated material.

The one-pack type coating agent is obtained by dispersing resin particles containing a terminal hydrazine structure-containing aqueous polyurethane (A) and a carbonyl group-containing vinyl polymer (B) into an aqueous medium, and the above aqueous polyurethane (A) is obtained by reacting a diisocyanate (a1) with a diol (a2) containing a polycarbonate diol (a21) and a carboxyl group-containing diol (a22) to obtain a polyurethane prepolymer (a) and thereafter performing neutralization of the polyurethane prepolymer (a) with a basic substance, chain extension with a hydrazine compound, and mixing with water, and the above diol (a2) contains 70-99 wt.% polycarbonate diol (a21). Its manufacturing method and the coated product are disclosed.