A wiring verification system is provided which is capable of simultaneously solving problems of wiring constraints on each board and of total skew in a wire passing through a plurality of boards. Board data, external connection board data, inter-board connection information, and wiring constraints are inputted in advance. When a system netlist creating unit (including a software means) creates a system netlist showing a theoretical connection relation of each board, an external connection tracing unit (including a software means) extracts external connection information based on the system netlist. An external load producing unit (including a software means) produces an external dummy load converted to a wire length or wire delay of the outside based on extracted external connection information. A wiring verification unit (including a software means) performs verification of a wiring state of an entire board by using the produced external dummy load. This enables proper distribution of wiring constraints on each board and solution of the total skew simultaneously.