PURPOSE: To contrive miniaturization of a data processing device, by a method wherein the title device has a printer within, which is made into a simple constitution by using a printing starting position sensor also for detection of a condition of an opening and closing door.

CONSTITUTION: A carriage 6 is moved leftward prior to starting of printing, a printing starting position sensor 15 abuts against a reference position instructing piece 19 and a movement is kept on until sensor output turns on. Hereupon, positional control of the carriage 6 is set to the initial. Then the carriage 6 is moved rightward, when an opening and closing door 12 is closed, an opening and closing transmission shaft 18 abuts against the opening and closing door 12, presses a turning lever 16 by being pressed in the opposite direction, the sensor 15 is worked by the turning lever 16 and the sensor output is turned on, through which the title device is warned of a matter that the opening and closing door is closed. When the sensor output is not changed, it is decided that the opening and closing door is opened, the carriage 6 is returned up to a fixed printing starting position and the printing is started.