To solve a problem that an entire optical filter including a main surface and a side surface is charged by static electricity generated by friction between the optical filter stored in a conveying tray with the conveying tray, and when the tray is conveyed when covered with a hermetic sheet and the conveying tray is unsealed, outside dust is attracted, and foreign matters can be deposited on the main surface of the optical filter.

The conveying tray of the optical filter formed of a crystalline material is sealed in a hermetic environment, and the humidity of the hermetic environment is kept at 50-65%.