Cyg X-3 is a well-known microquasar with a bipolar relativistic jet. Its famous giant radio outbursts have been repeated once every several years. However, the behavior of the millimeter wave emission has remained unclear because of limitations of time resolution in previous observations. We report here millimeter wave observations of Cyg X-3 experiencing giant outbursts with one of the finest time resolutions. We find a series of short-lived flares with amplitude of 1-2 Jy in the millimeter light curve of the 2008 April-May outburst. They have flat spectra around 100 GHz. We also find abrupt and large amplitude flux density changes with e-folding time of 3.6 minutes or less. The source size of Cyg X-3 is constrained within 0.4 AU and the brightness temperature is estimated to be $T_B gtrsim 1times10^{11}$ K.
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