A problem with conventional programmable display devices, in the case of attempting to edit screen data, is that screen data is externally extracted all at once and the extracted screen data is edited with drawing software. In order to resolve this problem, the present invention is provided with non-volatile memory (9) for storing multiple pieces of screen data created by drawing software; editing volatile memory (8) for storing input data; graphics volatile memory (7) for reading and storing desired screen data from within the multiple pieces of screen data stored in the non-volatile memory (9), as well as storing the input data of the editing volatile memory (8); display means (3) for displaying the desired screen data; and computation means (5) for obtaining the desired screen data and input data stored in the graphics volatile memory (7) and editing the obtained desired screen data in accordance with the obtained input data; wherein an edit mode takes effect in which the edited desired screen data is again displayed by the display means (3) and is again stored in the non-volatile memory (9) from the graphics volatile memory (7).