© 2017 by the American Helicopter Society International, Inc. All rights reserved. The wake flow of a small quadcopter unmanned aerial vehicle generates a ground effect during take-off and landing. The ground effect affects the rotor thrust and posture stability. However, the structure of the wake with plural rotors has not been unveiled experimentally. In this study, the wake flow structure of a quadcopter with flow interaction between rotors was examined, and the wakes of hovering were visualized using a laser light sheet. In addition, particle image velocimetry measurements were conducted, changing ground off height and the distance between rotors. The visualization results in several planes suggested a merging wake between rotors and pulled wake at the center of the quadcopter. Furthermore, the particle image velocimetry results showed the development of a soaring flow at the center of the quadcopter in the ground effect operation, and the velocity of the soaring flow decelerated with closing rotor distance. The experimental results indicate that the soaring flow pushes the quadcopter; this flow affects the lifting force on the quadcopter during the ground effect.