One embodiment of the present invention provides an opening/closing detection device, including: a plurality of sensors configured to be arranged along a predetermined portion of a mark attached to a vehicle; and a control unit configured to output an action trigger signal for instructing an opening action of an opening/closing body of the vehicle when detection signals representing a trace order of the predetermined portion are input from the plurality of sensors that detect an order of a motion of tracing the predetermined portion of the mark by a user of the vehicle.