PURPOSE: To eliminate the need to change the state of an input part by a user program by switching the state of the input part to a state corresponding to an input object window with an indication from the user program or an operator at the time of the switching of the input object window.

CONSTITUTION: An input device control part 2 controls the data input/output operations of respective input devices and informs the user program of the input data. A memory 20 is stored with data, programs, and input device information 2a required for the processes of a microprocessor 2b. When an active window is changed with the indication from the user program or by operator's operation, an active window ID from a multiwindow control part 4 is reported. It is judged whether the active window is already displayed and when not, the active window ID in input device information is changed to set an input device with input device state information.