PURPOSE: The light necessary for photosynthesis is fed effectively into the reaction tank to attain high efficiency of photosynthetic reaction.

CONSTITUTION: The photosynthesis reactor 1 composed of transparent inner walls 1a and transparent outer walls 1b is equipped with a plurality of tubular light irradiators 10 inside and an artificial light source 50 such as a fluorescent lamp inside the inner walls 1a, further equipped with air jetter 4 at the bottom of the reactor 1. The air including carbon dioxide is fed into the reactor 1 by means of the air jetter 4. Thus, the light is emitted from the source 50 to pass through the transparent inner walls 1a into the reactor where the light participates the photosynthesis, thus high efficiency of photosynthesis is achieved.