An electronic control device comprising: a plurality of electronic components (10, 12) including a first electronic component and a second electronic component; a substrate on which the plurality of electronic components are mounted; a case accommodating the substrate, on which the plurality of electronic components (10, 12) are mounted, in an accommodating chamber; and a connector mounted on the substrate and entering into the accommodating chamber from an opening portion of the case, the case and the connector cooperating with each other to form a fitting section through which the connector is fitted to the case, wherein the first electronic component has a height with respect to the substrate, which is higher than a height, with respect to the substrate, of the second electronic component, and the fitting section has a height with respect to the substrate, which is higher than the height, with respect to the substrate, of the first electronic component, the first electronic component is mounted on the substrate in a gap portion defined between the fitting section and the substrate, the fitting section includes a fitting insertion portion (52b; 152b; 252b), formed on the connector, and a fitting concave portion, formed on the case, to which the fitting insertion portion (52b; 152b; 252b) is inserted, the fitting concave portion is defined between an inner surface of the case and a fitting hold portion (36a; 136a) in a form of a horizontally protruding plate-like piece, protruding inward from inner surfaces of a side wall of the case, the fitting insertion portion (52b; 152b; 252b), in a form of a horizontal plate-like piece which protrudes outward from an upper portion of an extending wall extending forward from a sidewall of the connector and beyond a front wall of the connector, is inserted to the fitting concave portion, the case and the connector cooperate with each other to form an engaging section, causing the connector to engage the case, a hook-shaped protruding portion and a hook-shaped protruding portion cooperate with each other to define the engaging section placed widthwisely inside with respect to the fitting insertion portion (52b; 152b; 252b), wherein the hook-shaped protruding portion protrudes downward from an upper surface of a guide recess formed on an inner surface of a high upper wall portion of the case, and the hook-shaped protruding portion is formed on an upper wall of the connector, and the first electronic component is placed below the fitting hold portion (36a; 136a) in the gap portion. a plurality of electronic components (10, 12) including a first electronic component and a second electronic component; a substrate on which the plurality of electronic components are mounted; a case accommodating the substrate, on which the plurality of electronic components (10, 12) are mounted, in an accommodating chamber; and a connector mounted on the substrate and entering into the accommodating chamber from an opening portion of the case, the case and the connector cooperating with each other to form a fitting section through which the connector is fitted to the case, wherein the first electronic component has a height with respect to the substrate, which is higher than a height, with respect to the substrate, of the second electronic component, and the fitting section has a height with respect to the substrate, which is higher than the height, with respect to the substrate, of the first electronic component, the first electronic component is mounted on the substrate in a gap portion defined between the fitting section and the substrate, the fitting section includes a fitting insertion portion (52b; 152b; 252b), formed on the connector, and a fitting concave portion, formed on the case, to which the fitting insertion portion (52b; 152b; 252b) is inserted, the fitting concave portion is defined between an inner surface of the case and a fitting hold portion (36a; 136a) in a form of a horizontally protruding plate-like piece, protruding inward from inner surfaces of a side wall of the case, the fitting insertion portion (52b; 152b; 252b), in a form of a horizontal plate-like piece which protrudes outward from an upper portion of an extending wall extending forward from a sidewall of the connector and beyond a front wall of the connector, is inserted to the fitting concave portion, the case and the connector cooperate with each other to form an engaging section, causing the connector to engage the case, a hook-shaped protruding portion and a hook-shaped protruding portion cooperate with each other to define the engaging section placed widthwisely inside with respect to the fitting insertion portion (52b; 152b; 252b), wherein the hook-shaped protruding portion protrudes downward from an upper surface of a guide recess formed on an inner surface of a high upper wall portion of the case, and the hook-shaped protruding portion is formed on an upper wall of the connector, and the first electronic component is placed below the fitting hold portion (36a; 136a) in the gap portion.