In design of particularly large-scale, complicated semiconductor circuits, a two-dimensional graph is prepared with Si, for example, as one axis and Sj+Wmax+T as the other axis where T is a clock cycle, Wmax is the maximum delay of a circuit portion to be subjected to signal delay analysis, and Si and Sj are clock timings to registers to serve as an input and an output of the circuit portion. The delay analysis results of the circuit portion are plotted on the two-dimensional graph. Also, a two-dimensional graph is prepared with Si, for example, as one axis and Sj−Wmin as the other axis where Wmin is the minimum delay of the circuit portion, and the delay analysis results of the circuit portion are plotted on this two-dimensional graph. Using the resultant two-dimensional graph, therefore, it is possible to provide the cause or an indication for design improvement of the clock circuit, a hold error, and a set-up error.