Provided is a method capable of producing a retardation film suppressed in biaxiality, having a small Nz coefficient, and having a slow axis in an oblique direction with high production efficiency. The production method for a retardation film of the present invention includes: holding left and right side edge portions of a film to be stretched with left and right variable pitch-type clips configured to have clip pitches changing in a longitudinal direction, respectively; preheating the film; reducing, under a state in which a position at which the clip pitch of the clips on one side out of the left and right clips starts to reduce and a position at which the clip pitch of the clips on another side starts to reduce are set to different positions in the longitudinal direction, the clip pitch of each of the clips to a predetermined pitch to subject the film to oblique stretching; and releasing the clips holding the film.