To provide a projection optical device capable of shortening the time required for the mounting adjustment of plural optical display elements by simplifying a mechanism for adjusting the mounting position and angle of the optical display element.

Fixed plates 48 and 58 are fixed along three side surfaces of a cross dichroic prism 70. A liquid crystal panel for blue is mounted on one fixed plate without being adjusted. The liquid crystal panels 46 and 56 for red and green are mounted on adjusting plates 47 and 57. After the plates 47 and 57 are respectively moved along two other fixed plates 48 and 58 so as to adjust the positions and the angles of the panels 46 and 56 in a direction perpendicular to an optical axis, fixing pieces 47a, 47b, 57a and 57b projecting from the top and the bottom of the plates 47 and 57 are attached to the plates 48 and 58.