An optical system of a portable projector and a mobile communication terminal using the same are disclosed. The optical system comprises a light transmission member having first and second surfaces, a light source device for emitting light beams onto the first surface of the member, so as to allow the light beams to be transmitted into the member, and one or more optical elements supported on at least one of the first and second surfaces of the member for diffracting the light beams incident from the light source device into the member, and subsequently reproducing and emitting an image from the diffracted light beams, to the outside of the member.