Abstract: An adhesion device includes an adhesion sheet including an adhesion surface that is adherable to a biological surface, and a mounting surface located on a side opposite the adhesion surface; a device main body mounted to the mounting surface of the adhesion sheet; and a release sheet releasably adhered to the adhesion surface. The adhesion sheet includes a first portion to which the device main body is mounted, and a second portion to which the device main body is not mounted. The release sheet includes a release layer adhered to the adhesion surface of the adhesion sheet, and a folded layer formed of at least one layer and folded to a side, which is opposite to the adhesion surface with respect to the release layer, to be layered. The folded layer is layered on the release layer at least at a position of the second portion of the adhesion sheet.