center point of a circle formed by the filters 42 to 53 which are formed as described later such that the center point of the pattern coincides with the center shaft 54 the filters 42 to 53 are congruent with one another and arranged to be 30 degrees rotation symmetric about the center point of the pattern the color wheel 40 is preferably used as a so called scr system color wheel the second manufacturing method of the aforementioned color wheel 40 having spiral shaped filters will be described fig6 a and 6b show a masking jig which is used to demarcate filters in a process of forming filters to be described later the masking jig is shaped like a disk formed of a thin metal sheet processed by an electroforming method an etching method a laser machining method or the like and is referred to as a metal mask 70 in the description to follow below referring to fig6 a and 6b the metal mask 70 has four spiral shaped openings 62 to 65 congruent with one another and an insertion hole 66 the openings 62 to 65 are for demarcating filters of one color in the color wheel 40 the insertion hole 66 has a bore diameter slightly lager than the diameter of the center shaft 54 of the color wheel 40 and is usually formed by one of the above described methods enabling an accuracy of about 10 u03bcm the openings 62 to 65 and the insertion hole 66 are arranged such that the insertion hole 66 agrees with a center point of the pattern formed by the filters 42 to 53 demarcated.