To provide a slitting method of a battery separator-use resin film object that
is less susceptible to occurrences of holes and tearing at the time of a slitting
process. A slitting device, which is provided with a feeding roll 51 for feeding
a film that is wound up to a role with its rotational velocity being controlled,
a razor blade for slitting the film to a predetermined width, a sensor for detecting
a tension of the film and winding rolls for winding the film up while controlling
its tension, is used for carrying out a slitting process in a manner so as to satisfy
the following conditions (1) and (2): (Condition 1) 59.8104T/L59.8105
(Condition 2) 1R/T5 where L is a thickness (m) of the film
object, R is a rotational velocity (m/min) of the feeding roll and T is a tension
(N/m) of the film object after having been subjected to the slitting operation.
