To provide an ECU capable of simplifying the distribution of a wire harness, achieving the smooth assembling work and reducing the cost for components.

This engine control unit 2 provided with electronic components and various circuits for controlling an engine 1 is mounted approximately just above an intake manifold 1-3, an ignition coil circuit 2-17 and an injector circuit 2-16 are integrally formed on a case 2-1 of the engine control unit, and a connector 2-9 for a sensor circuit and a connector 2-6 for harness connection, connected to the engine control unit 2 are mounted on a peripheral wall face of the case 2-1 of the engine control unit.