An extremely large amount of volcanic gas has been released since mid-August 2000 from the volcanic island of Miyakejima, Japan, after formation of a summit. Variation of the SO₂ emission rate was monitored by repeated measurements with airborne COSPEC. In 2000, the SO₂ emission rate averaged at 42 kt/d, which is twice the global SO₂ emission rate from nonerupting volcanoes evaluated before this activity. The SO₂ emission rate gradually decreased to 7 kt/d by the end of 2002 and then remained constant until at least March 2004. The total SO₂ emission amounts to 19 Mt.