An insulating varnish usable for an insulating coat of an insulated wire on a conductor with a quadrangular cross section contains polyamide-imide resin varnish and organosilica sol mixed with the polyamide-imide resin varnish. The polyamide-imide resin varnish contains solvent and polyamide-imide resin. The organosilica sol contains dispersion medium and silica particles dispersed in the dispersion medium. Cyclic ketones having boiling point in a range of 130 to 180° C. make up 70 to 100 wt % or more of the dispersion medium.