Programmable Logic Controller(PLC) is the most widely utilized and plays an important role in industrial control system. The study about a PLC language is performed actively. Ladder Diagram(ID) is the most widely used in PLC. In is not suitable for describing a complex sequential logic and is very difficult to grasp the sequential flow of control logic and has the disadvantage for a maintenance. On the other hand, Sequential Function Chart(SFC) is very easy to grasp the sequential flow of control logic and has the compatability for a maintenance but has the disadvantage for describing a condition and a interlock logic. In this paper, we propose the method that describe the interlock logic using management step, and confirm his feasibility through a actual examples.