An integrator of an optical device using a color drum is disclosed. The integrator includes an opening receiving a light generated from a lamp, an optical path part reflecting and passing forward the light received at the opening, a mirror part refracting and totally reflecting the light passed through the optical path part and changing a direction of the light being transmitted, a polarization plate transmitting light rays having a constant polarization direction, among the reflected light, and reflecting remaining light rays having other polarization directions, and a wave plate changing a phase of the light reflected from the polarization plate.