To provide a water-based coating agent capable of improving rust-preventing properties of zinc-based plated steel or the like, having excellent film-formability, forming a coated film having electroconductivity, and applicable to a metallic component or the like of which antistatic properties are not preferable, and to provide the coated film.

The water-based coating agent containing colloidal silica and a styrene-butadiene copolymer (SBR) emulsion is regulated so that the weight ratio of the colloidal silica to the solid component of the SBR emulsion may be within the range of 10/90<(colloidal silica)/(SBR emulsion)<70/30, and contains a metallic filler of ≥5% expressed in terms of wt.% of the solid component.