An electronic control device includes: a board; a heat generating component mounted on the board; a heat conductive sheet thermally coupled to one surface of the heat generating component located on a side opposite to the board side; and a cooling mechanism thermally coupled to the heat conductive sheet. The heat conductive sheet includes a folded structure having a plurality of folded-back portions and a plurality of connection portions provided between the folded-back portions, and the plurality of folded-back portions of the heat conductive sheet is thermally coupled to each of the heat generating component and the cooling mechanism.