PURPOSE: To provide the subject method and system therefor enabling laterally slit films to be chucked on the chucking clip of a laterally drawing apparatus even if the films slit by a laterally splitting device are subjected to interspace widening and changed in width due to the variation in the longitudinal tension applied thereto.

CONSTITUTION: The entrance of a laterally drawing apparatus 30 is equipped with a laterally slit film lead-in device 6. The lead-in device, which is made up of a guide roll 6a provided the above entrance and a lead-in roll b set up so as to be pressedly subject to contact with the guide roll 6a, presents such function as to control the revolving speed of the lead-in roll 6b based on the signals from a film width detector 9 and lead the laterally slit films while narrowing the interspace of the films into the laterally drawing apparatus 30.