The purpose of the present invention is to provide a control unit whereby the quantity of a seal material to be used can be reduced, while ensuring waterproof performance. This electronic control device is provided with: a housing, wherein a plurality of members are bonded, and a peripheral end portion thereof is configured from a plurality of sides; a circuit board housed in the housing; and seal structures that are disposed along the sides at the peripheral end portion. A seal material is provided to the seal structures such that the members are connected to each other. The seal structures disposed on one side of the peripheral end portion are configured such that each of seal cross sectional areas at end portions of the side is smaller than a seal cross sectional area at a center portion of the side.