A cooling structure for a portable electronic device is provided, configured to accommodate, within a case having a sealing structure, a substrate on which a heat-generating component that generates heat during operation is mounted, and provided with a heat sink that diffuses the heat from the heat-generating component to a place away from the heat-generating component. The heat sink is integrated into an inner surface of an area corresponding to a front cover of the case or an inner surface of an area corresponding to a rear cover of the case, and a flat heat pipe flattened by being compressed in a thickness direction of the case is disposed such that one end is attached by being sandwiched between the heat-generating component and the heat sink while another end is arranged in close contact with the heat sink.