Nobeyama Radio Observatory, NAOJ, Minamimaki, Minamisaku, Nagano 384-1305, Japan

The Nobeyama Radioheliograph with temporal resolution of 50 ms (or 100 ms) has observed flares with sub-second time structures at 17 GHz. Some of them were initially analyzed and reported. In this report, we summarize results of our systematical analyses together with results of the previous analyses. Provisional results are that: (1) Their occurrence probability is small. (2) Their flux densities at 17 GHz are weak, less than 10 sfu. (3) Their durations (FWHM), rise times, and decay times range from 100 - 1000 ms, 100 - 300 ms, and 50 - 400 ms, respectively. (4) They occur at any stages of the impulsive phase. (5) Some of them show an excellent similarity in time profiles with the corresponding hard X-ray bursts. This also means that trapping of electrons is small. (6) The 17 GHz emission is emanated from the footpoint with stronger magnetic fields of a highly asymmetric loop. (7) If we assume rather strong magnetic field of several hundred Gauss, the 17 GHz flux is consistent with the corresponding hard X-ray spectrum. We suggest that the peak delay of the 17 GHz sub-second bursts with respect to the corresponding hard X-ray ones can be explained by pitch-angle dependence of electron propagation in a highly asymmetric loop.