PURPOSE: To improve efficiency and economics of cultivation, by providing a baffle wall in part of an endless water channel and water conduits passing below the wall, water propeller and gaseous carbon dioxide blowing inlets in the flow passage and further a recovery means for the gaseous carbon dioxide.

CONSTITUTION: In a cultivation apparatus for circulating and flowing microalgae, e.g. chlorella, etc., together with a culture fluid in an upward opened endless water channel 1, a baffle wall 3 is provided in part of the endless water channel 1 and water conduits 2 having deep bottoms are provided on both sides and under the baffle wall 3. A water propeller 6 and gaseous carbon dioxide blowing inlets 5 are provided in the water conduits 2 on the upstream side. Furthermore, a gas holder 4 is provided above the water conduits 2 on the downstream side and connected to gaseous carbon dioxide blowing systems 9 and 7 through a gaseous carbon dioxide recovery system 10.