PURPOSE: To provide a low cost labyrinth seal to prevent a worker from being troubled by management of the gap of the labyrinth seal, improve assembly properties and sealing performance, reduce weight, and improve reliability by a method wherein the labyrinth seal is fixed to the end face of a bearing holder subassembled on a sun gear shaft.
CONSTITUTION: A labyrinth seal 8 being an air seal is previously fixed to the end face of a bearing holder 7 subassembled on the sun gear shaft 13 of an impeller 1. The impeller 1 is assembled in a device even when a mounting error of a bearing holder 7 to a casing flange part 6, i.e., the mounting error of the rotary shaft of the impeller 1, is produced because of a backlash occurring to a thrust bearing 4, the bearing holder 7, the labyrinth seal 8, and the impeller 1 is not changed in a relation position in an axial direction. Thus, a labyrinth gap is kept at a constantly proper value between the properly set labyrinth seal 8 and the back of the impeller 1.