Abstract: A photosynthetic microorganism culture apparatus includes: a fermenter in which a culture solution including a photosynthetic microorganism is stored; a light incidence region through which light enters the culture solution being formed in the fermenter; one or a plurality of light sources that emit collimated light; a reflection mechanism that reflects the collimated light emitted from the light source in a predetermined direction as reflected collimated light; and a controller that causes the reflected collimated light reflected by the reflection mechanism to travel periodically in a previously-fixed direction to irradiate the light incidence region with the reflected collimated light.