Abstract: A mechanism for detacheably fitting a fixing member and an engaging member comprising a male fixing member having a head above a recessed neck of a smaller diameter and an engaging member comprising a hollow casing having an engaging body slidably fitted to the inside thereof by way of a resilient member. The fixing member and the engaging member are locked in a not-fit state by engaging the engaging body resiliently urged by the resilient member to the casing against the resiliency. The engagement between the engaging body and the fixing member in a not-fit state is released by bringing the engaging member and the head of the fixing member into press-contact, thereby engaging the elongate aperture of the smaller diameter in the engaging body and the neck of the fixing member, and locking them in a fit state by the resiliency of the resilient member. The frame main body and the resilient member are preferably molded integrally in the engaging body.