An electronic device includes: a casing; a board disposed inside the casing and having a heating element mounted thereon; an opposing member disposed inside the casing and having an opposing face opposed to a face of the board on which the heating element is mounted; a heat sink formed by alternately laminating thermal diffusion sheets and adhesive layers each having an opening at a location corresponding to the heating element on the opposing face of the opposing member; and a press member configured to press the heating element against a region of the heat sink corresponding to the opening of the adhesive layer, thus joining the thermal diffusion sheets together at the location of the opening.