A critical path detecting unit for detecting critical paths for a design in which cells are placed on an integrated circuit and information concerning timing constraints. A representative-critical-path extracting unit extracts a representative critical path by having one critical path represent critical paths which share more intervals than a certain number, and which are similar to one another, out of critical paths which have been detected by the critical path detecting unit. A path-image generating unit renders the representative critical path, which has been extracted by the representative-critical-path extracting unit and reflects information concerning other critical paths, which are similar to the representative critical path, on the representative critical path.