A tape reel assembly comprises a reel hub and flanges coaxially secured to, and extending radially outwardly from, opposite axial ends of the reel hub, respectively, each flange being molded by resin injection molding and having a tapered inside surface sloping down at a fixed taper angle from an inside periphery to an outside periphery thereof. The flange is molded by the use of an injection mold having a mold surface which borders at least a part of a mold cavity for configuration of the tapered inside surface of the flange and is convexly curved to the mold cavity.