In a reinforcing-film applying apparatus for use in production of separable slide fasteners, there are a first working station where a shaping die (50) and a coacting ultrasonic horn (49) are located, and a second working station where a heating die (78) and a coacting heating punch (77) are located, the first and second working stations being spaced apart remotely from one another along a longitudinal path (22) of a slide fastener chain (5). When one of successive pairs of blank tape portions (8) arrives at the first working station, a reinforcing film piece (9) is placed on the fastener chain (5) across the pair of blank tape portions (8), whereupon the shaping die (50) and the ultrasonic horn (48) are moved toward one another to fuse the reinforcing film piece (9) to the pair of blank tape portions (8) only at their inner marginal areas and also to shape such fused marginal portions so as to provide therealong a pair of pin-like members (10, 11) to which a pin and a box of a separable bottom end stop are to be attached. After that, when the pair of blank tape portions (8) with the reinforcing film piece (9) partially fused thereto arrives at the second station as the fastener chain (5) is further moved along the path (22), the heating die (78) and punch (77) are moved toward one another to apply pressure and heat to the pair of blank tape portions (8) and the reinforcing film piece (9) thereon at their superposed areas except the pin-like members (10, 11).