PURPOSE: To enable another system to use an interactive system without damaging the processing function dependent upon normal conversations by discriminating whether an interactive window on a display device is active or not to switch the data input/output destination between the interactive window and another device.

CONSTITUTION: When a main body processing part 2 of the interactive system waits for input, a window state discriminating part 4 checks whether an interactive window 8 is active or not and an input/output destination switching part 6 sets the interactive window 8 as the input/output destination if it is active; but otherwise, the switching part 6 sets another device or a medium 9 as the input/output destination. An input processing part 5 checks whether data is inputted from the switched input destination or not; and if it is inputted, required data is obtained from the input destination and data as processing results of the main body processing part 2 is outputted to the output destination. While the interactive window 8 is active, the normal interactive processing is performed because data is inputted and outputted from the interactive window 8; and while it is not active, the processing function of the interactive system is used through another device or the medium 9 by another system.