PURPOSE: To improve the program preparing efficiency by defining the relation of an input/output item and preparing a program with a two-dimensional defining means to set an input item and an output item.

CONSTITUTION: By a two-dimensional defining means 1, the item (input item) of an input means is set in the row direction of the two-dimensional table or the column direction of it and the item (output item) of an output means is set in the column direction or in the row direction, and the relation of the input means and the output means is stored in the position instructed by a column and a row. A program preparing means 2, when one input item is set to one output item, prepares an input output program to couple the input item and the output item, and when plural input items are set to one output item, the means prepares the input output program to couple plural input items and output items in accordance with the operation expression stored by an operation expression storing means 3. Thus, the program can be easily prepared and debugging is facilitated.