PURPOSE: To stably applying a reactive liquid, such as an instant film stiffener on a wet layer contg. a protein binding agent with low applied quantity and at high speed.

CONSTITUTION: A layer contg. a protein binding agent is formed on a supporting body 4. A coating liquid contg. a reactive liquid is caused to flow out at a flow rate of 0.4-0.7cc/cm.sec by an extrusion coater 3 to form a curtain film on the layer in a wet state. The height of the curtain film is adjusted so that the impact velocity may be 140-250cm/sec. A plate for shielding wind 2 is fitted near the curtain film on the upstream side and the application is made while the wind accompanying the coating liquid is shielded by the plate.