When urban areas are hit by a disaster such as an earthquake, subway and tunnel-collapsing causes severe damages to both people and property. Especially it requires a lot of manpower and time to rescue the buried persons in the scene of accident. Moreover, secondary damage can occur during the rescue operation by additional collapses. To detect buried victims in disaster situation, technologies that utilize images, sounds and radio signals are mainly used. However, they still require close access to the collapse site and the detection range of them is limited to small area. Because a rescuer has to look around a wide disaster scene, there is a difficulty in finding buried victims by missing Golden Time. To resolve this problem, in this paper we propose a stochastic method to estimate the location of buried persons in collapsing area using Wi-Fi signals. We assume that every victim in the disaster site has a smartphone. The method utilize only a few number of Wi-Fi signal receivers equipped on drones to make it available to detect victims' Wi-Fi signals in disaster situations. Our method can contribute to life protection technologies by providing the locations of buried persons for a quick rescue in case of a disaster.