PURPOSE: To reduce a check processing load with an applied program by controlling the input to a data processor for each input area with a data key and according to the information set at a control table when a control key is pushed.

CONSTITUTION: Character information is supplied by an input key 4, and an enter key 9 is pushed for production of a signal (e). This signal (e) is set at a register 17 via a control part 6. A discriminating part 18 detects the signal (e) within the register 17 and refers to an item d1 of a control table 14 to confirm that 1 is set there. Then the part 18 produces a signal OK to start a transmission/reception part 10. The key 9 is pushed again after input of the character information. Thus the part 18 refers to an items d2 of the table 14 to confirm that 0 is set there. Then the part 18 outputs a signal NG+F2. As a result, the input character information displayed so far at a display part 8 is inverted into a black display. Then an operating error is informed to an operator with inversion of the display color.