Wheelset rotational velocity variation in curved tracks causes measurement error of velocity, which leads to the error of the train location for the moving block system. Thus, clarifying the mechanism of rotational velocity variation is important to evaluate accuracy of the location detection for trains. To observe rotational velocity variation in a curved track, experiments and MBD simulations are conducted. The result of the experiments indicate that rotational velocity variation occurred, and the degree of variation of the front axle of the bogie is larger than the rear axle of the bogie. The result of the simulations shows the same tendency as the experiments, which suggests that the phenomenon of rotational velocity variation can be simulated. As the mechanism of rotational velocity variation, three factors are identified: rail length difference, variation of wheel rolling radius, and longitudinal creepage. To analyze the variation mechanism, a visualization method for the three factors is developed. The result of visualization suggests that the main reason for different variations between the front and the rear axle is the effect of different directions of longitudinal creepage.