An optical element includes a main body and a plurality of reflection structures. Two opposite ends of the main body are defined as a light input end and a light output end. The light input end has a groove. Walls of the groove are respectively defined as a first light input wall and a second light input wall. The main body has a total reflection surface located between the light input end and the light output end. The light beams entering the main body through the second light input wall can be totally reflected by the total reflection surface. The reflection structures are disposed on the main body and correspondingly located on the total reflection surface. The light beams entering the main body through the second light input wall can be totally reflected by two adjacent reflection structures and can be mutually staggered with each other.