To make arrangement of a hydraulic pump extremely easy, to significantly reduce weight thereof, and to reduce a manufacturing cost of a device.

The supercharger surplus power recovery device includes: a first internal combustion engine 1; a second internal combustion engine 13 disposed separately from the first internal combustion engine; a supercharger 5 rotary-driven by exhaust gas of the first internal combustion engine to supercharge charge air of the first internal combustion engine; a hydraulic pump 10 of a first fixed displacement type connected to a rotational shaft of the supercharger to be rotated together with the supercharger; a second hydraulic pump 11 of a first fixed displacement type connected to a crankshaft 2 of the first internal combustion engine to be rotated together with the crankshaft; a hydraulic circuit 20 connecting the first hydraulic pump with the second hydraulic pump; and a third hydraulic pump 12 of a variable displacement type disposed to the hydraulic circuit to control mutual hydraulic pressure flows between the first hydraulic pump and the second hydraulic pump, and connected to the crankshaft 14 of the second internal combustion engine to be rotated together with the crankshaft.