An electromagnetic wave detection apparatus comprising: an irradiator configured to emit electromagnetic waves; a first detector configured to detect reflected waves of the electromagnetic waves irradiated onto an object (ob); a propagation unit comprising a plurality of propagation elements (px) that, by irradiation position of the electromagnetic waves irradiated onto the object (ob), switch between propagating and not propagating the reflected waves of the electromagnetic waves towards the first detector; a memory configured to store related information associating an emission direction of the electromagnetic waves from the irradiator and two points on a path of the electromagnetic waves emitted from the irradiator to at least the propagation unit via the object (ob), the two points including an irradiation position and a position of a propagation element (px); and a controller configured to update the stored related information; characterized in that the related information comprises second related information associating the emission direction and the irradiation position of the electromagnetic waves emitted in the emission direction; and in that the controller is configured to update the stored related information by updating the stored second related information by updating a relationship between the emission direction and the irradiation position, based on a position of a propagation element (px) that is propagating the reflected waves towards the first detector and the emission direction of the electromagnetic waves corresponding to the reflected waves detected by the first detector from the irradiator. an irradiator configured to emit electromagnetic waves; a first detector configured to detect reflected waves of the electromagnetic waves irradiated onto an object (ob); a propagation unit comprising a plurality of propagation elements (px) that, by irradiation position of the electromagnetic waves irradiated onto the object (ob), switch between propagating and not propagating the reflected waves of the electromagnetic waves towards the first detector; a memory configured to store related information associating an emission direction of the electromagnetic waves from the irradiator and two points on a path of the electromagnetic waves emitted from the irradiator to at least the propagation unit via the object (ob), the two points including an irradiation position and a position of a propagation element (px); and a controller configured to update the stored related information; characterized in that the related information comprises second related information associating the emission direction and the irradiation position of the electromagnetic waves emitted in the emission direction; and in that the controller is configured to update the stored related information by updating the stored second related information by updating a relationship between the emission direction and the irradiation position, based on a position of a propagation element (px) that is propagating the reflected waves towards the first detector and the emission direction of the electromagnetic waves corresponding to the reflected waves detected by the first detector from the irradiator.