PURPOSE: To constitute so that a cursor is prevented from moving by a tab moving key to a tab position, which is positioned outside of a format area, by discriminating whether a cursor position and the tab position exist in the inside of the format area or its outside.

CONSTITUTION: A cursor position deciding part 16 discriminates whether a cursor exists in a position of the left outside or the right outside, in a cursor display area, by display area information from a line control part 14 and cursor position information from a cursor control part 15. In a tab position deciding part 17, tab position information, cursor position information and display area information of a line where the cursor is positioned, are obtained from a tab control part 13, the cursor control part 15, and the line control part 14, respectively, whether a tab position exists in the display area or not is discriminated, and its result is sent to a control part 12. The tab position being outside of the display area is not recognized as a tab position and is processed, and in case when the tab position is not set, the left end of the display area is regarded as a tab position and is processed.