In an electronic control device, semiconductor modules are disposed in a power region of a substrate, and on a surface of a substrate adjacent to a housing to radiate heat from rear surfaces to the housing through a heat radiation layer. Therefore, a heat radiation performance improves. Further, a first distance from an end surface of a power region corresponding part corresponding to the power region to the substrate is shorter than a second distance from an end surface of a control region corresponding part corresponding to a control region of the substrate to the substrate. Therefore, a closed circuit bridged by parasitic capacitances is formed mainly in an area of the power region and the power region corresponding part. A noise generated from the semiconductor modules is returned to noise sources through the closed circuit without affecting the control region.