A rotary system comprising: a first rotary machine including a first rotary shaft; a second rotary machine including a second rotary shaft; and an intermediate shaft device including: an intermediate shaft main body having a first end portion connectable to the first rotary shaft and a second end portion connectable to the second rotary shaft, the intermediate shaft device being configured to rotate about an axis; and a pair of radial bearings (13, 14) slidably supporting a first shaft portion and a second shaft portion of the intermediate shaft main body, the first shaft portion being disposed at the first rotary shaft side of the intermediate shaft main body and including the first end portion, and the second shaft portion being disposed at the second rotary shaft side of the intermediate shaft main body and including the second end portion, wherein a third shaft portion of the intermediate shaft main body between the first shaft portion and the second shaft portion is solid, and wherein a radial dimension of the third shaft portion of the intermediate shaft main body is greater than radial dimensions of the first shaft portion and the second shaft portion of the intermediate shaft main body which are supported by the pair of radial bearings (13, 14), characterized in that the rotary system further comprising: a lubricating oil supply unit supplying a lubricating oil to the pair of radial bearings (13, 14), the lubricating oil supply unit being connectable to another lubricating oil supply unit of the first rotary machine and the second rotary machine, and a box-shaped exterior member disposed to cover both the intermediate shaft main body and the pair of radial bearings (13, 14). a first rotary machine including a first rotary shaft; a second rotary machine including a second rotary shaft; and an intermediate shaft device including: an intermediate shaft main body having a first end portion connectable to the first rotary shaft and a second end portion connectable to the second rotary shaft, the intermediate shaft device being configured to rotate about an axis; and a pair of radial bearings (13, 14) slidably supporting a first shaft portion and a second shaft portion of the intermediate shaft main body, the first shaft portion being disposed at the first rotary shaft side of the intermediate shaft main body and including the first end portion, and the second shaft portion being disposed at the second rotary shaft side of the intermediate shaft main body and including the second end portion, an intermediate shaft main body having a first end portion connectable to the first rotary shaft and a second end portion connectable to the second rotary shaft, the intermediate shaft device being configured to rotate about an axis; and a pair of radial bearings (13, 14) slidably supporting a first shaft portion and a second shaft portion of the intermediate shaft main body, the first shaft portion being disposed at the first rotary shaft side of the intermediate shaft main body and including the first end portion, and the second shaft portion being disposed at the second rotary shaft side of the intermediate shaft main body and including the second end portion, wherein a third shaft portion of the intermediate shaft main body between the first shaft portion and the second shaft portion is solid, and wherein a radial dimension of the third shaft portion of the intermediate shaft main body is greater than radial dimensions of the first shaft portion and the second shaft portion of the intermediate shaft main body which are supported by the pair of radial bearings (13, 14), characterized in that the rotary system further comprising: a lubricating oil supply unit supplying a lubricating oil to the pair of radial bearings (13, 14), the lubricating oil supply unit being connectable to another lubricating oil supply unit of the first rotary machine and the second rotary machine, and a box-shaped exterior member disposed to cover both the intermediate shaft main body and the pair of radial bearings (13, 14). a lubricating oil supply unit supplying a lubricating oil to the pair of radial bearings (13, 14), the lubricating oil supply unit being connectable to another lubricating oil supply unit of the first rotary machine and the second rotary machine, and a box-shaped exterior member disposed to cover both the intermediate shaft main body and the pair of radial bearings (13, 14).