Evidence for a Source Size of Less than 2000 AU in Quasar 2237+0305

Recently, OGLE team have reported clear quasar microlensing signal in Q2237+0305. We have analyzed the microlens event of ``image C'' by using their finely and densely sampled lightcurves. From lightcurve fitting, we can unambiguously set the source size of \ 0.98 Einstein Ring radius as a conservative limit. This limit corresponds to 2000 \ (AU), if we adopt M\ lens \~ 0.1M\ obtained by a recent statistical study of mean mass of lens object. This gives a clear evidence for the existence of an accretion disk in the central region of the quasar.