The present invention has as an object to render a photochromic coating layer free from air bubbles and obtain a uniform layer without film thickness unevenness in the coating layer. In the prevent invention, entrained air in a coating fluid stored in a vessel of a coating unit comprising the vessel, a check valve for preventing back-flow of the coating fluid connected to the vessel, and optionally an ejection nozzle connected to the check valve; air existing inside of the check valve; and optionally air existing inside of the ejection nozzle are removed by plugging an outlet of the coating fluid existing downstream of the check valve and then rotating the coating unit on an axis of the vessel and orbiting the coating unit on a revolution axis simultaneously.