The invention relates to a radiation measuring device, especially for measuring high power radiation (10), comprising a measuring window (12) and a deflecting unit which can guide at least one part of the radiation which is to be measured (10) from the measuring window (12) to a sensor unit (14). According to the invention, the deflecting unit comprises at least one bar (16) into which the radiation (10) is injected via the measuring window (12), parallel to the longitudinal extension (18) thereof, via a side (70). The radiation is retransmitted along the longitudinal extension of the surface (18) bar to the sensor unit (14).