Disclosed is a key sheet efficiently diffusing local heat generated by a device mounted on a board. A key sheet has a base sheet formed of a rubber-like elastic material in which a heat conductive filler is mixed. Thus, if a semiconductor device on a board generates heat, it is possible to suppress local heat storage by the heat conductive filler of the base sheet. Further, there is no need to provide a separate member for heat diffusion between the board and the key sheet, making it possible to realize a reduction in thickness. Thus, with the key sheet, it is possible to meet the requirement for heat diffusion to eliminate local heat storage in electronic apparatuses, and the requirement for a reduction in the thickness and weight of electronic apparatuses.