PURPOSE: To detect the printing state of a printer by observing roll-up of display picture only, through the picture control in synchronizing with the printing of the printer.

CONSTITUTION: Data inputted from an input device 1 is stored in a memory incorporated with a controller 6. In displaying one picture's share of a document stored in the memory on a CRT display 2, when a print instruction is given from the device 1, the printing is made from the head of the document with a printer. When the printer 4 completes the printing of the one line at the head of the document, the device 6 gives a line feed instruction to a printer controller. Thus, the printer 4 makes line feed. The controller 6 transmits a roll-up instruction to a CRT controller 3. The controller 3 receives this instruction and rolls up the document displayed on a display 2 for one line's share of the printer 4. The device 6 picks up a new line from the memory and inserts the line to the lowermost line of the display 2.