A printing device including a processor, a print-head, a carriage, a mask and a sensor is provided. The processor controls the operation of the printing device. The print-head fixedly configured in the printing device prints on an object. The carriage includes a fixing device for fixing the object. The carriage carries the object fixed thereon and moves relative to the print-head. The mask placed on the object has a hole for defining a printable area of the object. The sensor senses to obtain information including a position of the carriage and the printable area of the object. The information is provided for the print-head to print on the object within the printable area while the object is moved to below the print-head.