Managing commands that have not been executed is simplified while maintaining a state in which real-time commands can be executed. A printer 2 has a write control unit 21A that writes received commands to a receive buffer 31, a command execution unit 21B that executes the written commands, and a real-time command execution unit 21C that executes written commands that are real-time commands. The printer 2 enters a full-buffer mode as needed by the capacity of available storage space in the receive buffer 31, and when in the full-buffer mode the write control unit 21A cyclically writes commands to an auxiliary space created in the receive buffer, and the real-time command execution unit 21C reads and executes real-time commands from the auxiliary space.