The method includes obtaining, using a face camera of a smart phone, identification information from a ceiling light of a facility with visible light communication, and obtaining location information of the ceiling light related to the identification information. The method also includes displaying a location related to the location information of the ceiling light on a map of the facility on a display of the smart phone. The smart phone is set on a cart in a state that the face camera is directed to a ceiling of the facility on which the ceiling light is attached, and the face camera is a CMOS sensor and the CMOS sensor is used only for the visible light communication.