PURPOSE: To prevent a coating material from spreading to outside parts and enhance the yield of product, by a method wherein a pair of auxiliary nozzles are provided at positions proximate to a measuring nozzle to blow air from the sides of both end faces in the width direction of a belt form material.

CONSTITUTION: In the vicinity of a position for blowing air from the measuring nozzle to the belt form material, the auxiliary nozzles 10, 11 are provided so as to blow air 8' to the end faces 9 in the longitudinal direction of the material 4 from the outside of the end face parts. Air is supplied from an air supplying device 12 to the measuring nozzle to measure the quantity of a coating material applied to the material 4 and, simultaneously, air 8' is blown off also from the auxiliary nozzles 10, 11 through a branched pipe 15. By air 8' thus blown, air from the measuring nozzle is prevented from spreading outward at the end parts in the width direction of the material 4. Accordingly, the coating material is restrained from spreading to the outside, and the coating material is completely prevented from creeping around to the end face side.