Gumma , prefecture (1990 pop. 1,966,287), 2,446 sq mi (6,335 sq km), central Honshu, Japan. Maebashi is the capital; other important cities are Isezaki, Kiryu, and Takasaki. The prefecture is mountainous and has many hot springs. Gumma's economy is based on the production of wheat and raw silk. Sulfur and manganese are also mined.