Cylindrically converging shock waves have been produced by detonating 20‐cm‐diam explosive shells in atmospheric air. Shadowgraphs were taken to monitor the production of waves. A spectroscopic measurement of temperature was made using a monochromator combined with a photomultiplier. The spectral radiant energy was compared with the blackbody function (Planck’s law). The dependence of temperature upon the initiation energy (the chemical energy of explosives) was also investigated. It was shown that temperature was approximately proportional to the square root of the initiation energy. The attained temperatures ranged from 13 000–34 000 K depending on the initiation energy. These are 3500–9500 K lower than those estimated from shock propagation speeds. The implosion pulse duration (the half‐value width) of 2.0–2.5 &mgr;s was observed. A possibility of the further increase of temperature as well as some problems was suggested.