To realize the improvement of flame retardance on an outer surface and the cost reduction of a finished product by laminating by coextrusion a flame-retardant insulating resin layer of flame retardant polybutylene terephthalate as an outermost layer and a heat bonding resin layer as an innermost layer.

A flame-retardant insulating resin layer (thickness: 70μm), with an outermost layer comprising 100 pts.wt. of polybutylene terephthalate blended with 40 pts.wt. of ammonium polysulfate as a flame retardant and 5 pts.wt. of silicon dioxide as a flame retardant assistant, is coextruded into a film using a feed block T-die. In addition, a heat bonding resin layer (thickness: 70μm) consisting of maleic acid-modified polyolefin (190°C MFR: 3.5, DSC melting point: 125°C) is laminated on the inner face of the flame-retardant insulating resin layer to obtain a film for flat cable with a gross thickness of 140μm. The alternate use choice for the modified polylefin is a polyester heat bonding resin.