PURPOSE: To enhance the resistance against chemicals of a timing belt by furnishing a reinforcing fiber band with aux. fiber bands with high chemical resistance on both sides of the reinforcing band across its width, and inserting straight in a plastic member so that the aux. fiber bands are exposed at the two side edges.

CONSTITUTION: Aux. fiber bands 24 whose warps are made of polypropylene fiber with high chemical resistance are placed at both side edges of a reinforcing fiber band 14 woven from warps of Alamid fiber, and they are put in a cavity 20 of No.1 metal die 16, whereon No.2 metal die 18 is placed, and polypropylene is poured from a runner 22 to perform insert molding. Here the aux. fiber bands 24 shall protrude at both side edges of the belt, and after molding, the protrusion is cut off. This enhances the resistance against chemicals.