Design time (TAT) is reduced in a layout design of a semiconductor integrated circuit having a well supplied with a potential different from a substrate potential. A layout design method of the present invention includes preparing a first cell pattern placed on a semiconductor substrate of a first conductive type, preparing a second cell pattern having a deep well of a second conductive type, placing the first cell pattern in a first circuit region, and placing the second cell pattern in a second region different from the first circuit region. This reduces TAT in chip design.