Map of Japanese provinces (1868
) with Mimasaka Province highlighted
Mimasaka Province (美作国 Mimasaka-no kuni) or Sakushu (作州 Sakushū) was an old province of Japan in the area of Okayama Prefecture on the island of Honshū.
The province had borders with Bitchū, Bizen, Harima, Hōki, and Inaba Provinces.
The ancient capital city of the province was Tsuyama.
View of Mimasaka Province, woodblock print by Hiroshige
In 713 (Wadō 6, 3rd month), the land of Mimasaka was separated from Bizen Province.
Mimasaka was the home of the samurai Miyamoto Musashi who is known for writing The Book of Five Rings.
In the Meiji period, the provinces of Japan were converted into prefectures. The maps of Japan and Mimasaka Province were reformed in the 1870s.
Nakayama jinja was the chief Shinto shrine (ichinomiya) of Mimasaka. 
Media related to Mimasaka Province at Wikimedia Commons