An illumination optical apparatus and a projection type display apparatus capable of preventing an image on boundary lines of a fly-eye lens from deviating from a designed position and preventing unevenness of brightness is provided: wherein a first lens holding member holding said first fly-eye lens; a second lens holding member joined to said first lens holding member, and holding said second fly-eye lens; and a third lens holding member joined to said second lens holding member, and holding an optical lens are provided; and said first lens holding member and said second lens holding member are joined to be relatively rotatable about an optical axis.