A portable electronic device comprising: a housing; an antenna module that is disposed in a vicinity of an inner surface of the housing with a gap from the inner surface; and a first heat diffusion member that is provided in the housing to be separated from the inner surface of the housing and is thermally connected to the antenna module, wherein a path through which heat generated by the antenna module is transferred along the first heat diffusion member, is separated from the inner surface of the housing; wherein the housing includes a pair of main surface portions (11a, 11b) and a plurality of side surface portions connecting the pair of main surface portions, the antenna module is disposed in a vicinity of the inner surface of the side surface portions with the gap from the inner surface, and the first heat diffusion member is disposed along one main surface portion of the pair of main surface portions while being separated from the inner surfaces of the pair of main surface portions and the plurality of side surface portions; the portable electronic device further comprises a second heat diffusion member provided in the housing and thermally connecting the antenna module and the first heat diffusion member; a circuit board that is provided in the housing; a first heat generating element that is provided on the circuit board; and a third heat diffusion member that is provided in the housing and disposed to be separated from the inner surface of the side surface portion, wherein the first heat generating element is thermally connected to the third heat diffusion member; and wherein the circuit board is provided with a second heat generating element, and the second heat generating element is thermally connected to the first heat diffusion member. a housing; an antenna module that is disposed in a vicinity of an inner surface of the housing with a gap from the inner surface; and a first heat diffusion member that is provided in the housing to be separated from the inner surface of the housing and is thermally connected to the antenna module, wherein a path through which heat generated by the antenna module is transferred along the first heat diffusion member, is separated from the inner surface of the housing; wherein the housing includes a pair of main surface portions (11a, 11b) and a plurality of side surface portions connecting the pair of main surface portions, the antenna module is disposed in a vicinity of the inner surface of the side surface portions with the gap from the inner surface, and the first heat diffusion member is disposed along one main surface portion of the pair of main surface portions while being separated from the inner surfaces of the pair of main surface portions and the plurality of side surface portions; the portable electronic device further comprises a second heat diffusion member provided in the housing and thermally connecting the antenna module and the first heat diffusion member; a circuit board that is provided in the housing; a first heat generating element that is provided on the circuit board; and a third heat diffusion member that is provided in the housing and disposed to be separated from the inner surface of the side surface portion, wherein the first heat generating element is thermally connected to the third heat diffusion member; and wherein the circuit board is provided with a second heat generating element, and the second heat generating element is thermally connected to the first heat diffusion member.