PURPOSE:To reduce the operation time while a flashing is made possible during the motoring by checking outputs by a breaking in using a normal fuel after a fuel restriction through a motoring. CONSTITUTION:After the assembling of an engine 2, the rotating shaft thereof is connected to a motor 1 to forcibly drive the engine 2 at a specified rotational frequency. At the same time, a flashing oil is injected into a lubrication system from a flashing oil feed tube 10. The rotation of the engine 2 permits the enhancing of a flashing effect thereby removing chips or the like in channels effectively. Fuel from a fuel tank 3 is fed to a fuel injection pump 5 via a flow detector 4 and it is controlled through a flow meter 8 to keep the injection at a set value. Then, after a further fuel control corresponding to a mechanical loss through a torque meter, outputs are checked for by a breaking in using a normal fuel. This can reduce the operation time while enabling a flashing during the motoring.