When a Shinkansen train runs through a tunnel at a high speed, pressure developed outside the train shows substantial fluctuations which lead to pressure change inside the train. In order to prevent aural discomfort among passengers, it is necessary to estimate these pressure changes for the Shinkansen train which has a ventilation system with continuous draught. In this paper a numerical method for calculating pressure is shown using the method of characteristics. Calculations are performed on running tests of Shinkansen trains Series 100 N and 300 and the calculated results are compared with the measured ones. The results show that the numerical method simulates well the pressure changes outside and inside a Shinkansen train running through a tunnel, and countermeasures to alleviate aural discomfort should be taken in cases of trains traveling at a higher speed.