The X-ray photometer RF is designed to measure the solar X-ray radiation in the soft spectral range. In addition to continuous monitoring of the solar radiation in the X-ray range, the instrument can be used as an indicator for automatic switching-on of the scientific instrumentation for registering the processes of the active solar events, assuming a change in the solar X-ray radiation as a precursor of these phenomena. The photometer is oriented along the -Z-axis of the subsatellite, i.e. toward the Sun. The photometer consists of two units: the detector unit and electronics unit. The photometer is the scintillating detector with an aluminium foil in front of it to prevent penetration of soft particles and X-rays. The output signal is passed to the two-channel amplitude analyzer where it is selected in two ranges: 10-15 keV and 15-60 keV. The impulses from the channels with a fixed amplitude are transferred to the electronics unit where they are accumulated during 0.8 s (time of one exposure step). The maximum capacity of the detector is 183441 impulses/0.8 second, so for higher flux intensity (which is hardly probable) the detector data are not valid.