PURPOSE: To reduce a change in thickness irregularity and to dispense with the monitoring' of thickness and width and the adjustment of a cap during manufacturing in forming a film, by using the cap having width of 400mm or more and setting the emitting amount of a polymer from the cap to 300kg or more/hr and setting the slit gap of the cap to 0.8-5.0mm.

CONSTITUTION: The thickness of a formed polypropylene film like article is measured in the lateral direction thereof and the respective deviations of the thickness profile of the polypropylene film like article corresponding to the positions of the respective adjust bolts of a cap and an objective thickness profile are calculated. The slit gaps of the cap at the positions of the respective bolts are adjusted corresponding to said deviations to prepare the polypropylene film like article. At this time, the cap having width of 400mm or more is used and the emitting amount of a polymer from the cap is set to 300kg or more/hr and the slit gap of the cap is set to 0.8-5.0mm.