A heat transfer device is provided. The heat transfer device includes a first heat conduction sheet and a second heat conduction sheet. The first heat conduction sheet includes two first rigid parts and a first bendable part connected between the two first rigid parts. The second heat conduction sheet includes two second rigid parts and a second bendable part connected between the two second rigid parts. The two first rigid parts are thermally coupled to the two second rigid parts, respectively. The first bendable portion includes a nonlinear section.