An optical element includes a bottom surface, a total reflection surface above the bottom surface, a recess recessed from the bottom surface toward the total reflection surface and first and second light exit surfaces. The optical element has a central axis perpendicular to the bottom surface. The total reflection surface has a peripheral boundary away from the central axis. The first light exit surface is connected to the peripheral boundary of the total reflection surface and extends toward the bottom surface away from the central axis. The second light exit surface is connected to the first light exit surface, extends away from the central axis, and is connected to the bottom surface. Each of the first and second light exit surfaces is consisted of at least one linear sub-refractive surface. Each linear sub-refractive surface is a straight line in any cross section passing through the central axis.