A fixing device capable of being fixed, by simple fixing, to a living body without causing an occurrence of inflammation is provided. The fixing device 3 is fixed beneath the skin of the living body and includes a porous portion 31a capable of inducing cells thereto and a flat portion 31b that allows the cells to be adhered thereto, the porous portion 31a and the flat portion 31b are provided adjacent to each other, and a virtual surface SF1 of the porous portion 31a and a surface SF2 of the flat portion 31b are substantially flush with each other.