[en] The SIGMA installation used for studying pion minus radiative scattering on nuclei is described. The particle beam with the momeitum of 40 GeV/c produced at the accelerator internal target is focused on a studied target. The flux of particles on the target is determined using scintillation counters. Pions minus are separated by means of the differential and threshold gas Cherenkov counters. Coordinates and angles of particles are measured by means of scintillation hodoscopes with space coding and two sets of proportional chambers. Pion minus detector consists of a scintillation hodoscope (five counters having dimensions of 100x10x1 cm) and Cherenkov total absorption counters covering the area of 50x100 cm. Pion minus momentum are measured by means of the magnetic spectrometer consisting of a magnet, a system of proportional chambers and a system of spark chambers. According to a trigger signal the data from beam monitors, scintillation hodoscopes, proportional and spark chambers and Cherenkov counters is recorded into the SUMMA system units and then transmitted to the HP-2100 computer through a special interface. The computer provides on-line control over the equipment operation, data recording on a magnetic tape and realizes the event geometrical reconstruction and physical analysis. Measurement of incident particle tracks by two independent systems (hodoscopes and proportional chambers) gives an opportunity to check continuously the efficiency of each system and provides precise track timing. The accuracy of incident particle coordinate and angle measurement constitute correspondingly 0.6 mm and 0.11 mrad