To provide a design automation device which can design a circuit diagram using address allocation information and information about data bus width, and can design the circuit diagram efficiently with few mistakes.

CPU and peripheral IC device, which a developer mounted, are selected, and address space allocation and data bus width are set using an address allocation device 16. The address allocation device 16 outputs IC address information 15 including address space allocation information and data bus width information. A circuit diagram design device 14 automatically connects the selected CPU and the peripheral IC device and designs a system circuit diagram 13 using registered data of a symbol library 17, a block library 18, and an IC information library 19 besides the IC address information 15.