A gas expansion system comprising: a first expansion turbine (37; 37a; 37b) including a first rotating shaft, a first impeller attached to the first rotating shaft and configured to, when the first rotating shaft rotates, expand a gas while taking the gas into the first impeller, a first bearing portion supporting the first rotating shaft, a first gas supply passage through which bearing gas is supplied to the first bearing portion, and a first gas discharge passage through which the bearing gas which has been supplied from the first gas supply passage to the first bearing portion is discharged from the first bearing portion; and a second expansion turbine (38; 38a; 38b) including a second rotating shaft, a second impeller attached to the second rotating shaft and configured to, when the second rotating shaft rotates, expand a gas while taking the gas into the second impeller, a second bearing portion supporting the second rotating shaft, a second gas supply passage (387; 399) through which the bearing gas is supplied to the second bearing portion, and a second gas discharge passage through which the bearing gas which has been supplied from the second gas supply passage (387; 399) to the second bearing portion is discharged from the second bearing portion, wherein the first expansion turbine (37; 37a; 37b) and the second expansion turbine (38; 38a; 38b) are connected to each other in series such that the gas expanded by the first impeller of the first expansion turbine (37; 37a; 37b) is supplied to the second impeller of the second expansion turbine (38; 38a; 38b), characterized in that: the first gas discharge passage and the second gas supply passage (387; 399) are directly connected to each other such that the bearing gas discharged from the first gas discharge passage is directly supplied to the second gas supply passage (387; 399). a first expansion turbine (37; 37a; 37b) including a first rotating shaft, a first impeller attached to the first rotating shaft and configured to, when the first rotating shaft rotates, expand a gas while taking the gas into the first impeller, a first bearing portion supporting the first rotating shaft, a first gas supply passage through which bearing gas is supplied to the first bearing portion, and a first gas discharge passage through which the bearing gas which has been supplied from the first gas supply passage to the first bearing portion is discharged from the first bearing portion; and a first rotating shaft, a first impeller attached to the first rotating shaft and configured to, when the first rotating shaft rotates, expand a gas while taking the gas into the first impeller, a first bearing portion supporting the first rotating shaft, a first gas supply passage through which bearing gas is supplied to the first bearing portion, and a first gas discharge passage through which the bearing gas which has been supplied from the first gas supply passage to the first bearing portion is discharged from the first bearing portion; and a second expansion turbine (38; 38a; 38b) including a second rotating shaft, a second impeller attached to the second rotating shaft and configured to, when the second rotating shaft rotates, expand a gas while taking the gas into the second impeller, a second bearing portion supporting the second rotating shaft, a second gas supply passage (387; 399) through which the bearing gas is supplied to the second bearing portion, and a second gas discharge passage through which the bearing gas which has been supplied from the second gas supply passage (387; 399) to the second bearing portion is discharged from the second bearing portion, wherein a second rotating shaft, a second impeller attached to the second rotating shaft and configured to, when the second rotating shaft rotates, expand a gas while taking the gas into the second impeller, a second bearing portion supporting the second rotating shaft, a second gas supply passage (387; 399) through which the bearing gas is supplied to the second bearing portion, and a second gas discharge passage through which the bearing gas which has been supplied from the second gas supply passage (387; 399) to the second bearing portion is discharged from the second bearing portion, wherein the first expansion turbine (37; 37a; 37b) and the second expansion turbine (38; 38a; 38b) are connected to each other in series such that the gas expanded by the first impeller of the first expansion turbine (37; 37a; 37b) is supplied to the second impeller of the second expansion turbine (38; 38a; 38b), characterized in that: the first gas discharge passage and the second gas supply passage (387; 399) are directly connected to each other such that the bearing gas discharged from the first gas discharge passage is directly supplied to the second gas supply passage (387; 399). the first gas discharge passage and the second gas supply passage (387; 399) are directly connected to each other such that the bearing gas discharged from the first gas discharge passage is directly supplied to the second gas supply passage (387; 399).