PURPOSE: To easily and accurately position the optical constituent component of the liquid crystal color projecting device.

CONSTITUTION: The positioning mechanism consists of a couple of side plates 35 and 36 which are positioned in parallel opposite each other across the optical constituent component and have 1st positioning holes 38a and 39a positioned opposite each other and bored at the fitting position of the optical component and 1st positioning pins 43 and 43b which are inserted into the 1st positioning holes 38a and 39a and abut on the incidence surface of the optical constituent component to position the optical constituent component and also maintains the parallelism between both the side plates 35 and 36. Thus, the optical constituent component is precisely positioned to the hole precision of the positioning holes 38a and 39b and the diameter precision of the positioning pins 43a and 43b and sufficient precision is obtained at the end of the assembling press.