PURPOSE: To quickly regain remembrance up to a previously interrupted part and to immediately proceed to read the remainder by displaying a part being displayed when interruption occurs.

CONSTITUTION: When a display interrupt command is inputted from an input part 60, a group number 22 in accordance with text group data 21 being displayed on a display part 30 is stored in the prescribed area of a storage part 20. After that, when a user inputs a display start command from the input part 60 to restart display, a retrieval part 40 reads the group number 22 stored in the prescribed part of the storage part 20, and retrieves an explanatory text information index 23 in accordance with the group number, and finds the existence of explanatory text data 24 in accordance with document group data 21 by a pointer 25, and displays the explanatory text data 24 on the display part 30. The content of the text group data 21 in the storage part 20 in accordance with a read group number is displayed based on the read group number following the explanatory data 24.