A design method of a semiconductor integrated circuit sets an area having apices of opposing corners of a position of a start point logic cell and a position of an end point logic cell to a repeater search area, adds free area information to the repeater search area, sets a drive boundary in the repeater search area based on a drive ability of the start point logic cell, searches a repeater candidate that can be arranged in an area of the drive boundary based on the free area information, calculates a delay time from the start point logic cell to the end point logic cell based on delay time information and a coordinate of the repeater candidate that is searched, and determines a repeater arranged between the start point logic cell and the end point logic cell from the repeater candidate based on the delay time that is calculated.