In an element wherein a plurality of ridges (16, 36) are arranged in parallel, supports (17, 37) are formed to sandwich each of the ridges (16, 36). More specifically, on an outer side of the ridge (16) in the element, the first support (17a) is formed, and on an inner side in the element, the second support (17b) is formed. On an outer side of the ridge (36) in the element, the first support (37a) is formed, and on an inner side in the element, the second support (37b) is formed. Thus, even when a resist is applied on an element surface and spin-coating is performed at the time of manufacturing the element, the resist on the inner side than the ridges (16, 36) in the element can be prevented from flowing into a groove between the ridges to a certain extent by means of the second supports (17b, 37b), and a resist film thickness on the inner sides of the ridges (16, 36) in the element can be prevented from being considerably small compared with that on the outer sides in the element.