An optical unit for projection type image display apparatus, by which the occurrence of registration deviation can be restrained and projected images of high contrast can be obtained, is disclosed. This optical unit comprises a first optical element which performs at least one of color separation and color combination; a holding member attached to the first optical element; and a second optical element which optically acts on one of incident light on the first optical element and emergent light from the first optical element. The linear expansion coefficients a1, a2, and a3 of the materials forming the first optical element, the second optical element, and the holding member have the following relationship: a1