The present disclosure generally relates to a signal transmission path evaluation device and method for evaluating EMC resistance of a signal transmission path using a computer system. An operating device of the computer system is input with signal transmission line shape data, signal transmission line path data, signal transmission line shape dispersion data, and margin information for noise input of a communication device connected to the signal transmission line. Calculations are performed including an electric field or a magnetic field in a vicinity of the signal transmission line path from the signal transmission line path data, dispersion of the signal line transmission line shape via a random number, noise waveform at a communication device input from the electric field or the magnetic field in the vicinity of the signal transmission path, error occurrence determination, and error rate from plural time trial results. Information concerning the calculated error rate is output.