PURPOSE: To provide a projector which is free from the change of the focal distance due to the rise of temperature of a CRT by setting a positive lens right before a negative lens consisting of a cooling liquid and a shell lens.

CONSTITUTION: The temperature of a shell lens 2 rises up together with a CRT cooling liquid 3 having the satisfactory heat transmittance by the heat generated on the surface of a CRT 1 after the projection is started. At the same time, a metallic barrel 5 releas the heat of the liquid 3 and also raises the temperature of a positive lens 8 with the heat transmission. Thus the refractive indexes of the liquid 3, the lenses 2 and 8 are reduced by the rise of the temperature. At the same time, the positive power of the lens 8 is reduced together with the negative power of a negative lens consisting of the liquid 3 and the lens 2. Thus, both powers are offset with each other and the total focal distance of a projection lens does not change. Thus it is possible to provided a projector which is free from the change of a video screen.