To provide an engine which makes it to connect electric component products mounted on the engine body to harnesses, and subsequently mount them on the engine body previously, in a process to be performed before loading the engine on a working machine, and simplifies connection work necessary when the engine body and the electric component products mounted on the engine body are inspected.

The engine 100 includes: a rail pressure sensor 85; injection actuators 83, 83, ...; a differential pressure sensor 78; an exhaust gas temperature sensor 79; and an ECU 600 which is connected to these sensors and actuators through harnesses, respectively, and controls the engine 100. In the engine, all the plurality of harnesses are connected to the ECU 600 via a relay connector panel 400 mounted on the engine 100.