PURPOSE: To discriminate display contents at an index display part without depending upon a main display screen by allowing a main display output processing circuit and an index display output device circuit to operate independently of each other.

CONSTITUTION: A display control part 4 is equipped with an input processing circuit 10 which processes signals from a keyboard input part 1 for specifying classifications from an interface circuit 5, keyboard input part 2 for specifying item numbers, and keyboard input part 3 for requesting display requests to obtain input signals for discrimination, and an input processing circuit 11 which processes a signal from a keyboard input part 6 for specifying TAG numbers from an interface circuit 7 to obtain an input signal for discrimination. To those circuits 10 and 11, a discrimination circuit 12 which outputs an index display data signal on the basis of the signals for discrimination are connected. To this discrimination circuit 12, a TAG table 13, index display output processing circuit 14, and main display output processing circuit 15 are connected.