In the present study, 50 m-range distance and position measurement method for autonomous flight device such as four-rotor drone by using two searchlights was proposed, and the precise distance/position measurement performance was evaluated in an outdoor situation. To realize over 10 m long-distance flight of the drone under unstable GPS signal situations such as under the bridge or inside tunnels for periodic inspections, the correct self-position measurement is important for the stable control. This study is to propose a simple method of over 50 m range autonomous four-rotor helicopter movement control using high power 300W two searchlights as InfraRed sources on the ground and the direction of the searchlights sets to the investigation target position such as bridge side. High power light sources of the two searchlights are enabled to measure the correct drone position via an attached drone's camera with an InfraRed filter, and it realizes 1.5 m standard deviation position estimation error when 50 m distance in an outdoor daylight situation. In addition, the limitation of the position detectable condition also measured and analyzed in other experiments. Our proposed method would be effective in the situation that there is no skilled the drone control operator and the flight by visual confirmation of man are hard conditions, and useful to develop the position measurement system with low cost.