It is well known that when a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the distant exit, a micro-pressure wave is radiated from the exit portal toward the surrounding area. In addition, several pressure waves are radiated toward the outside area from the entrance when a train enters the tunnel and from the exit when the train leaves it. We call the former a tunnel entry wave, and the latter a tunnel exit wave. Although the tunnel entry/exit wave is normally weaker than the micro-pressure wave, they could cause an environmental problem with increases in the train speed. In this paper, fundamental characteristics of the tunnel entry/exit wave are described based on the results of field tests, model experiments and simple acoustic analysis.