An electromagnetic wave detection apparatus (10) includes an irradiator (11), a first detector (17), a propagation unit (20), a memory (13), and a controller (14). The irradiator (11) irradiates electromagnetic waves. The first detector (17) detects reflected waves of the electromagnetic waves irradiated onto an object (ob). The propagation unit (20) includes propagation elements (px). By irradiation position of the electromagnetic waves irradiated onto the object (ob), the propagation elements (px) switch between propagating and not propagating the reflected waves towards the first detector (17). The memory (13) stores information related to the emission direction of the electromagnetic waves. The controller (14) updates the information related to the emission direction based on the position of the propagation element (px) that is propagating the reflected waves toward the first detector (17) when the first detector (17) detects the reflected waves.