To reduce the intensity of the singing by non-uniformly forming the size of ruggedness in a labyrinth part to disperse the frequency of the singing to be generated by the eddy formed in the labyrinth part.

A labyrinth 5 is provided on an inner circumferential side of a diffuser adapter 3 of a fairing part to reduce the leak flow returned to a suction side by a part of the fluid boosted by a rotating impeller. The frequency of the vibration caused by the eddy is changed by disturbing the shape of the uniform eddy generated between fins by irregularly changing the height of the fins at the labyrinth 5 and by changing the clearance between the diffuser adapter 3 and an impeller shroud 2. The uniformity of the shape of the eddy formed in the labyrinth 5 is lost when the leak flow passes the labyrinth 5, and the frequency of the vibration caused by the eddy does not agree with the natural frequency of the material forming the fairing part to prevent generation of the singing due to the eddy.