Major sound sources remaining for Shinkansen, after the development and use of various noise reduction techniques, are the pantographs and bogies. Although aerodynamic sound generated from the bogies is highly influenced by air flow under the vehicle, velocity profiles under the vehicle on slab track have not been obtained since they are difficult to measure in field tests. In this study, we installed 8 simplified hot-wire anemometers on a slab track along the sleeper direction (at right angles to the direction of the rails) to measure time histories of velocity under vehicles. The ensemble averaged velocity for each type of rolling stock with different operation speeds clarified the characteristics of under-floor flow. The results and discussion are summarized as follows: (1) for series E5, the velocity at the track center, when non-dimensionalized with the train operational speed, is about 0.3 to 0.4, (2) for series E2, the velocity at the track center is about 0.4 to 0.5, which is 0.1 higher than that of series E5, (3) after increasing at the forward bogie section, the flow velocity decreases toward the rear section, again being driven up at the rear bogie section. This successive process, in which about a 0.1 increase is observed for series E2 and E5, is repeated with constant amplitude. This is probably because the channel of the flow under the vehicle, as it passes into the bogie section, immediately was enlarged which resulted in the decrease of velocity. These valuable results would be helpful not only for the aerodynamic sound evaluation but also for the validation of numerical simulations.