The heat sink is provided perpendicularly to a bottom of a case of an on-board information device as the electronic device and adjacent to a right side plate of the case having windows (104) and (105). The heat sink includes grooves each vertically extending from the first to the third heat generating elements at a lower portion upward, and the through holes formed at positions corresponding to the windows of the right side plate of the case and at the upper portion of the heat sink along the grooves.