A heliostat 5 for use in a sunlight concentration system for utilizing sunlight as energy according to this invention has a plurality of small concave mirror elements 8 and reflects and focuses sunlight reflected off the individual concave mirror elements to a light concentration portion as if upon reflection off a single large concave mirror 9. The angles of the concave mirror elements 8 are changed to define a single concave mirror having a predetermined curvature. When the incident angle of sunlight with respect to the concave mirror is large, the curvature is reduced (like a shallow dish). When the incident angle is small, the curvature is increased (like a deep dish).