Provided is a circuit board design system for designing a circuit board which is mounted with a semiconductor component and is with a cable connected to it. The circuit board design system comprises: an input means which inputs board design information on a circuit board; an EMI characteristic derivation means which derives a characteristic of EMI generated from the circuit board, on the basis of the board design information; a storage means which stores a cable length correction characteristic for deriving the EMI characteristic; and an output means which outputs the EMI characteristic derived by the EMI characteristic derivation means. The EMI characteristic derivation means comprises: an analysis model creation means which creates a simplified analysis model provided with a simplified virtual cable, as an analysis model of the circuit board, on the basis of the board design information; a board analysis means which calculates virtual cable current flowing in the virtual cable by performing electromagnetic field analysis of the simplified analysis model; and an EMI calculation means which calculates actual cable current flowing in the cable by the use of the virtual cable current and the cable length correction characteristic and then calculates a characteristic of EMI radiated from the cable by the use of the actual cable current.
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