A collimating lens includes a first end face with an LED accommodation hole for accommodating an LED lamp, a second end face, which is disposed opposite to the first end face and has an area greater than the first end face, and a sidewall, which is connected between the first end face and the second end face and has a first wall section and a second wall section. The second wall section extends from the second end face toward the first end face to a predetermined distance. The first wall section having one end connected to the second wall section and the other end extending toward the first end face to a predetermined distance. The first wall section defines with the second wall section a contained angle smaller than 180.degree..
