PURPOSE: To effectively culture algae, etc., in an ideal state for photosynthetic culture by supplying light from the side surfaces of optical fibers as a side surface lighting means and simultaneously also supplying carbon dioxide.

CONSTITUTION: Light having a suitable intensity is supplied from a side light- emitting means 12 and carbon dioxide is also supplied around the emitted light from a carbon dioxide gas-supplying means 13 disposed together with many light-transmitting fibers 16 in a fine bubble state, whereby photosynthesizing plants such as algae, etc., are suitably cultured in a culture solution in the coexistence of the light and the carbon dioxide gas.