A method for manufacturing a refilled cartridge is provided for performing refilling of printing material after use of a cartridge comprising a chamber of variable capacity, a detection section that optically detects the printing material inside the chamber, an air introduction port that introduces outside air into the chamber, a valve section that opens and closes the air introduction port according to the negative pressure inside the chamber, and a supply port that supplies the printing material within the chamber to the outside. With this manufacturing method, the printing material is refilled into the chamber so that a designated volume of air exists after refilling of the printing material is completed.