A method of manufacturing an obliquely stretched long film includes an oblique stretching step and a tension application step. In the oblique stretching step, a long film is stretched in an oblique direction with respect to a width direction into a stretched film (F). In the tension application step, while the stretched film (F) is being drawn along a longitudinal direction, a tension in a drawing direction is applied to the stretched film (F). Here, in the tension application step, the tension in the drawing direction of the stretched film (F) is changed in the width direction, and thus the stretched film (F) is drawn.