Provided is a stretched film manufacturing method wherein when manufacturing a stretched film by hot stretching in at least one direction a composite film (100), which is obtained by respectively forming, on one edge and the other edge of a film in the width direction, a first edge and a second edge from a thermoplastic resin that differs from the thermoplastic resin configuring the central portion of the film by melt-extrusion from a forming die (220), the following formulas (1) and (2) are satisfied when, of cut sections in the width direction of the composite film (100) prior to hot stretching, the cross-sectional area of the first edge is A1 [m2] and the cross-sectional area of the second edge is A2 [m2], the coefficient of static friction between the first edge and the second edge and gripping members during hot stretching is µ, the gripping force of the first edge and the second edge by the gripping members is F [N], and the stretching stress per unit cross-sectional area of the second thermoplastic resin during hot stretching is σ [N/m2]. A1 < µF/σ --- (1) A2 < µF/σ --- (2)