This paper presents a study of the gateway access-point selection problem for the wireless infrastructure mesh network (WIMNET). WIMNET is a wireless mesh network composed of multiple access-points (APs) that communicate mutually using radio transmissions, and all the traffics to/from the Internet go through the limited number of gateway APs. Thus, the selection of these gateway APs often determines the whole performance of WIMNET, because heavy congestions at gateway APs and their peripheries can drastically increase the delay and the link failure due to radio interferences. In this paper, we define a cost function to minimize the total traffic in WIMNET in order to reduce congestions and present a simple algorithm. Through simulations using the newly developed WIMNET simulator, we show the effectiveness of our approach.