To perform excellent-operability conversion by simultaneously performing a conversion instruction of an arrangement of vertical writing and horizontal writing, and a conversion instruction of a format such as a font.

This document display device has: a sentence display means displaying an inputted sentence by the vertical writing or the horizontal writing; a storage means storing the inputted sentence; an instruction means instructing whether displaying the sentence stored in the storage means by the vertical writing or the horizontal writing; and a conversion means converting a display direction into a display direction instructed by the instruction means. The document display means has: a format setting means capable of setting the format by the vertical writing or the horizontal writing in time of vertical writing display or horizontal writing display; and a format conversion means converting the display direction by the conversion means, and simultaneously, converting the format into the set format.