PURPOSE: To make the lubricating oil of a turbocharger appropriate to the sliding conditions, by providing an oil supply passage for only the turbocharger, separately from an oil supply passage for an engine itself.

CONSTITUTION: The main shaft 1 of a turbocharger is supported by a bearing portion 10 provided between a turbine chamber 2 and a compressor chamber 4. Lubricating oil is supplied to the bearing portion 10 through a pump 31, an oil supply pipe 33 and an oil supply port 13 so that the oil circulates through an oil drain port 14 and a filter 30. since the lubricating oil of the turbocharger circulates through an oil supply passage separate from that for an engine itself, the oil is not deteriorated by the blow-by gas of the engine or by the like and is kept clean for a long period of time.