A branching point on a wire is detected in the layout results S101. A
delay amount of a route with a dummy buffer being inserted on a wire
subsequent to the branching point S102 and that of the route without a
dummy buffer being inserted are then calculated S103. Based on the delay
amounts, an insertion point at which a load-dividing buffer is to be
inserted is determined S104. On condition that a load-dividing buffer is
to be inserted at the insertion point, the drive capability of a driving
cell preceding the insertion point is calculated so that timing
constraints are satisfied S105. Then, after it is confirmed that a
load-dividing buffer is insertable at the determined insertion point
S106, processes of placing a load-dividing buffer, changing the drive
capability of the driving cell, and changing wiring information are
performed on the layout results S107.