An automatic trace shaping method comprises the steps of: setting sets of coaxial equiangular octagons each having sides parallel with a predetermined reference line; performing a process for tentatively disposing the traces each having segments passing between the adjacent vias so that such segments overlap any sides of the equiangular octagons that are set for the vias existing at positions nearest to such segments sequentially for each trace so that at least clearance can be secured from the trace for which the process has been completed immediately before; and performing a process for further correcting positions of the tentatively disposed traces that cannot secure the clearance from the other adjacent tentatively disposed traces so that at least the clearance can be secured from such other tentatively disposed traces sequentially in an order inverse to that in the tentative disposition process for the traces.