PURPOSE: To provide a gear driven multishaft turbocompressor, capable of increasing total efficiency and total pressure ratio at the same number of revolutions.

CONSTITUTION: In a range of high pressure stages II, III of this gear driven multishaft turbocompressor having impellers 25 arranged forward and backward along a flow, two or more compressor impellers 25 are provided on a pinion shaft 6 via a disc diffuser 9 in the dame direction of flow. An intermediate cooler 24 is provided between an intermediate discharge casing 13 and an intermediate intake nozzle 4. Gas flows into the impeller 25 from an intake nozzle 7 at the stage II and flows out again from the compressor via the intermediate discharge casing 13. After being cooled intermediately on the outside, gas flows into the stage III again via the intake nozzle 4, is discharged after passing via the second impeller 25, and flows out from this stage through a casing 2. In a radial expander, similar arrangement for stages Ia, IIa, IIIa is utilized by reversing the direction of the flow of gas.