PURPOSE: To prevent generation of coating defects due to dropping of a coating material deposited on a collector cover.

CONSTITUTION: A mist shutter 1 is connected with a piston in a hydraulic cylinder 2 and pushed by the piston to the position shown as a dotted line between a collector cover 3 and an aluminum substrate 4. The substrate 4 is fast rotated to control the thickness of the coating material, and after completing that, the mist shutter 1 is driven to be inserted between the cover 3 and the substrate 4. Thereby, even when a coating material splashing from the substrate and depositing on the collector cover 3 drops, the coating material is prevented from dropping by the mist shutter and from depositing on the aluminum substrate 4.