Abstract: There is disclosed a device for aiding in designing a semiconductor integrated circuit wherein a circuit converter converts a circuit to be subjected to automatic placement and routing which is stored in a circuit storage into a new cell which is then registered in a cell library storage by a cell generator while the changed circuit is stored in an equivalent circuit storage in the form of an equivalent circuit, on the basis of which a circuit verifier stimulates a circuit operation. A placement and routing unit performs cell placement of the equivalent circuit and cell-to-cell routing by using the cell library storage storing the specification of the new cell, whereby the integrated circuit having good performances such as area, operating speed, and power consumption is designed without difficulty.