To provide a storable winding core in which an insulating film can be formed easily even at a corner without applying an insulating tape or an insulating material to the winding core in production of a coil for clock, and to provide a kit for forming a coil winding core insulating film without using a sheet, and a clock using the same.

A kit for forming an insulating film of a coil winding core comprises (A) a coating agent containing at least an imidazole derivative having a melting point of 100°C or higher in the solvent, and (B) a polymerization liquid including at least an epoxy monomer having a melting point of 20°C or lower. Alternatively, a kit for forming an insulating film of a coil winding core comprises a coating agent containing, as a binder in the coating liquid of (A), epoxy resin having a melting point of 100°C or higher, and (B) a polymerization liquid including at least an epoxy monomer having a melting point of 20°C or lower.