This disclosure discloses a printer (1) comprising a USB port (P), memory (36) having a regular storage area (40) which a host (111) connected to the USB port (P) is able to recognize as a removable drive, printing means (54, 55, 56) configured to perform printing based on print data produced by an application program, and a processor (32) configured to control the printing means (54, 55, 56) and the memory (36), wherein the regular storage area (40) includes a first memory area (41) in which an executable file of the application program is stored, and at least a second memory area (42, 43) in which at least an instruction file including the print data is able to be written, and wherein when the executable file of the application program is read and executed by the host (111), the processor (32) executes a plurality of processing while concurrently performing at least one processing thereof for the instruction files, the plurality of processing including file write processing for updating a content of original instruction file stored in the second memory area (42, 43) by writing the instruction file received from the host (111) in the second memory area (42, 43), update preparation processing for enabling to be updated later a content of the instruction file stored and held in the second memory area (42, 43) after the file write processing ends, and print processing for making the printing means (54, 55, 56) execute printing of print data corresponding to the instruction file written in the second memory area (42, 43) by the file write processing.