Method for manufacturing long obliquely stretched film

A method for manufacturing a long obliquely stretched film has an obliquely stretching step in which both ends of a supplied long film in the width direction thereof are gripped by grippers arranged at equal intervals, the long film is conveyed while the grippers are moved at a constant speed along opposing rails, and the long film is stretched in the direction oblique to the width direction by changing the conveyance direction of the long film during the conveyance. At the position at which the obliquely stretching step terminates, a line which connects opposing grippers is substantially parallel to the width direction of the long obliquely stretched film.