To arrange a slightly closed part, such as a casing, on a support such that it does not meet user's eyes and momentarily meets the user's eyes.

An automatic fastener operated through passage of it through a dead center has a base part 1. A bow-form tongue part 2 rotatably coupled to the base part 1 is coupled to a lug 3 through a hinge 6. Further, the fastener has an external protrusion part 10 to form a support point for bringing the lug 3 into a dissociation position, i.e., a release lock position. The fastener is applicable when a part formed in a box-shape or a channel-form shape is securely locked on a support or a member in such a manner not to meet user's eyes.