PURPOSE: To prevent the contamination of a culture chamber by placing a high-performance filter in a path for passing a gas to be circulated through the culture chamber.

CONSTITUTION: The culture box 1 is provided with a main body 5 having a culture chamber 7 holding a specimen such as cell and maintained at a prescribed temperature, a feeding apparatus to feed a gas such as carbon dioxide gas to the culture chamber 7 of the main body and keep the concentration of the gas at a prescribed level, a path 13 connecting the upper part and the lower part of the culture chamber 7 and a blower 16 placed in the path to circulate the gas through the culture chamber 7. A high-performance filter 17 is placed in the path 13.