MITSuME Telescope Observation of GRB080506

We report the multicolor early afterglow observation of a 200 s-long GRB080506 with the 50 cm MITSuME Telescopes at Akeno and Okayama, Japan. We started observations of the afterglow at 117 s after the trigger at Akeno when the prompt emission was still ongoing, and 253 s after the trigger at Okayama. We find no counterpart for the X-ray flare in the optical light curve, implying that the X-ray and optical emission in the early afterglow have different origins. We also found a temporal break at about 1000 s in the optical light curve, which we interpret as the passing of the spectral peak at v,, and derive constraints on the physical parameters based on the synchrotron shock model. The SED in the optical band suggests a significant absorption in the host galaxy, well fitted with the LMC dust model with E(B - V) similar to 0.2 and redshift z similar to 2.2.