A polyvinyl acetal resin varnish which is so low in stimulus property, toxicity, environment-polluting property, offensive odor, and inflammability that no problem is caused in practical use, and which is high in safety, low in viscosity, and thus favorable in workability, and an application of the polyvinyl acetal resin varnish are provided. As an organic solvent for dissolving the polyvinyl acetal resin, there is used a nonaqueous solvent, preferably carbonate ester, and more preferably a mixed solvent composed of cyclic carbonate ester and chain carbonate ester, into which the polyvinyl acetal resin is evenly dissolved regardless of its type, resulting in varnish which is high in safety and low in viscosity. Since the varnish has an action of gelling the organic solvent, the varnish can be used as a gelling agent in various applications.