1. A method for designing a cell layout of a semiconductor integrated circuit, comprising the steps of: determining whether a layout of priority cells is completed; performing a layout of general cells when the layout of the priority cells is judged to be completed in the step of determining whether the layout of the priority cells is completed; and outputting a layout result of each of the priority cells and the general cells; wherein a layout of the priority cell comprises the steps of: inputting cell layout information and priority cell information from information files storing the cell layout information and the priority cell information; extracting a layout cell width, a limit of a layout area width, and an arranged area width based on the cell layout information and the priority cell information; setting the arranged area width to zero; extracting the width of a cell to be arranged; calculating a target layout position and X direction of a layout of the cell to be arranged based on the cell layout information and the priority cell information; and comparing the total of the width of the cell to be arranged and the arranged area width with the limit of the layout area width to determine whether the total of the widths is larger than the limit of the layout area width, wherein, when the result of the comparison step is that the total of the widths is larger than the limit of the layout area width, the method comprises the steps of: shifting the target layout position in the Y direction and inverts the direction of the layout of the priority cell in the X direction; determining whether the priority cell can be arranged at the target layout position; if the cell can be arranged, setting the arranged area width to zero; and if the cell cannot be arranged, tracing back up to a priority cell having a layout option while cutting off priority cells already arranged, wherein, when the result of the comparison step is that the total of the widths is not larger than the limit of the layout area width, the method comprises the steps of: determining whether the priority cell can be arranged at the target layout position; if the cell can be arranged, adding the width of the cell to be arranged to the arranged area width and shifting the target layout position in the X direction; and if the cell cannot be arranged, performing the steps for the case where the result of the comparison step is that the total of the widths is larger than the limit of layout area width.