To lighten the burden of data modifying method specification on an operator and reduce errors in input by setting the input form of parameters of control data according to the result of retrieval from a data base and changing the parameters.

An input processing is carried out by a direct input processing part 27 or select input processing part 28. An input method decision part 25 decides which of the direct input processing and select input processing is performed according to input information and the contents of a modification information data base 26 and supplies an execution command for the input processing to a corresponding input processing part 27 or 28. In the modification information data base 26, input conditions, check data, etc., by the parameters are set in addition to decision information. Consequently, troublesome condition input for data modification becomes unnecessary. Further, an input state is thus automatically set with check data like this way and then the operator accepts input through fixed input, so that a data modifying method is standarzied.