PURPOSE: To allow document data which corresponds to a displayed form to be output again regardless of a change of printing media by updating a buffered document format in accordance with current printing pitch width information.

CONSTITUTION: Data is input by an action indicator key and if printing is requested, a document format which is written in the format area FORMAT of RAM 3 is copied into a printing format storage RAM 8. Right and left margin position data are read from RAM 3, the left margin position data is subtracted from the right margin position data, and the difference is divided by a printing pitch width. After this, it is determined in which position in a display section 6 the right margin corresponds, and the printing pitch width is multiplied by the quotient. At the same time, the left margin position data is added to the product to update the position of a right margin mark. A value obtained by subtracting the left margin position data from each tabulation position value by the number of tabulation settings in the printing format storage RAM 8, is divided by printing pitch width. Then the printing pitch width is multiplied by the quotient and the left margin position data is added to the product to update each tabulation position. Printing data of a single line is transferred to a line buffer LB and document data is printed by a printing section 4.