1. An electronic control device, comprising:a housing which is joined by a plurality of members and of which a peripheral portion is configured by a plurality of sides;
a circuit board which is accommodated in an inside of the housing; and
a seal structure which is disposed on the peripheral portion along the sides, wherein
a liquid seal material is applied to the seal structure and cured so as to connect between the plurality of members, and
wherein a seal sectional area in an end portion of a side is smaller than that in a central portion of the side in the seal structure which is disposed on the side of the peripheral portion.