PURPOSE: To execute clock distributing work within a short time and to minimize the influence of a clock skew by executing the layout of a circuit by a layouter in accordance with circuit describing information including an inputted order circuit and distributing clock by circuit position information obtained as the result of layout.

CONSTITUTION: At first, a clock distributing part 1 reads out circuit describing information 2 and executs opimum clock distribution based upon positional information 4 applied from the layouter 3. The layouter 3 inputs circuit description 5 and then executes its layout. Thed layout result is checked and simulated to confirm whether the layout circuit is driven like a designer's purpose or not. When the circuit is a satisfied circuit, the processing ends. When the circuit is not satisfied, information relating to the position of the circuit is extracted from the layout result and sent to the distributing part 1 to execute clock distribution again.