PURPOSE: To facilitate operator's operation by displaying a block diagram indicating current processing and a list of programmable function keys which are effective in the current processing on the display of a terminal.

CONSTITUTION: In an interactive system wherein an operator at the terminal advances processing in an interactive mode with a center device, the terminal is provided with a key STATE for requesting the display of the block diagram and a key SHOW PE for requesting the display of the list of programmable keys. When the key STATE is depressed, th block diagram for showing the position of current processing is displayed on the display screen of the terminal. When the key SHOW PE id depressed, the list of the programmable function function keys which are effective in the current processing is dipslayed on the display screen of the terminal.