We report an outburst of a black hole X-ray binary, V4641 Sgr in 2004 July. We succeeded in performing time-series photometry during the outburst, which showed repetitive short flares having a timescale of 10 min. Even after the outburst, it remained active for 17 d, as observed after an outburst in 2002. In conjunction with a low X-ray flux, we suggest that the 2004 outburst has the same nature as those in 2002 and 2003, though the total released energy during the outburst seems to be less in 2004.