A mounting structure of an LED includes an LED unit including an LED, a lens element in front of the LED, and a collar around the lens element; a support member including a through-hole through which the lens element of the LED unit is exposed and an annular portion; an annular contacting surface formed on one of the annular portion as an annular concave surface and the collar as an annular convex surface; an annular contacting portion, formed on the other of the annular portion and the collar, wherein an orientation of the LED unit is adjusted by changing a relative contacting position between the annular contacting surface and the annular contacting portion; and a fixing device which fixes the LED unit to the support member while maintaining the contacting position of the annular contacting surface and the annular contacting portion after the adjustment.