A PLC system construction support tool is provided wherein a display 31 of text and numeric values is produced at the left of a paste board 22. The display 31 is provided for each row of a system and whenever a unit is added or deleted, the numeric values are updated. The display 31 contains a character string of "WIDTH" meaning the total length of the units on the corresponding row and the numeric value of the width (mm units), a character string of "CURRENT CONSUMPTION" meaning the total current consumption of the units on the corresponding row and the numeric value of the current consumption (mA units), and a character string of "WEIGHT" meaning the total weight of the units on the corresponding row and the numeric value of the weight (g units).