A long obliquely stretched film is obtained having an orientation axis in a direction with an angle θs of 10° or more and 85° or less from a width direction by grasping both side ends in the width direction of a longitudinally stretched film with an average retardation Re1 by grasping means; stretching the film under a condition that a long obliquely stretched film sample with an average retardation Re2 (Re2 is smaller than Re1) can be obtained and traveling speeds of the grasping means are substantially equal at the film both side ends through a preheating zone, a stretching zone and a fixing zone; releasing the both side ends of the film from the grasping means; and taking it up around a winding core.