To provide a turbo compound engine surely protecting a power turbine, even if an accelerator is deeply stepped down in a state of not sufficiently rising in hydraulic pressure of a lubricating system in starting.

This turbo compound engine transmits motive power recovered by the power turbine to a crankshaft via a hydraulic coupling 9. An oil losing means for losing engine oil 15 in the hydraulic coupling 9 in the starting, comprises a normally opening control valve 17 arranged in the middle of a supply line 16 for supplying the engine oil 15 as a working fluid to the hydraulic coupling 9, and a control device 18 for continuously closing the control valve 17 until oil feeding delay time passes by reading out the oil feeding delay time to the power turbine from an oil feeding delay time map on the basis of at least any one of hydraulic pressure of the lubricating system and the water temperature of a water cooling system in the starting.

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