Method for manufacturing long stretched film

This method for manufacturing a long stretched film has a long film formation step, an oblique stretching step, and a winding step, an oblique stretching device has a heating furnace and a gripper travel support tool, and the stretching direction of the oblique stretching device can be arbitrarily changed, the gripper travel support tool is provided with a drive shaft, and in the oblique stretching step, a long film is continuously heated by a planar heater provided between the drive shaft and the long film in at least a stretching zone inside the heating furnace.