To ensure and improve the credibility of the fastening and retaining function of easily demountable fastening and retaining parts performing the function when a plurality of parts, members and equipment are fastened and retained at a normal use time with a shape memory alloy and releasing the function by the shape recovery of the alloy.

A head part 11, a shaft 12, and an inner diameter expanded part 13 are provided in the fastening and retaining parts. In a fastening and retaining state, a member 14 with a spring property is inserted in the expanded part, thereby reinforcing the mechanical strength shortage of the martensitic phase of the alloy.