A damper is provided which can more reliably prevent malfunction and breakdown and which enables efficiently performing repair and inspection operations. This damper, provided with a casing linked to a first object and a rotating part linked to a second object rotatably attached to the first object, damps rotation in either the direction closing or the direction opening the second object, and is provided with a sensor which detects prescribed change in the external environment in the damper or around the damper, and a control unit which externally communicates, over a communication network, information relating to the change in the external environment detected by the sensor, wherein the sensor is configured from at least one of: a rotation sensor for detecting the number of revolutions of the rotating part; a sound sensor for detecting sound during rotations of the rotating part; a temperature sensor for detecting temperature; and a torque sensor for detecting torque on the basis of friction during rotation of the rotating part.