To restrict the structure length of an underground structure part by having a hollow piston provided with a stroke cylinder opened toward an adjusting rod, and storing a thrust bearing in the hollow piston.

An adjusting mechanism 10 includes an adjusting rod 13, and the adjusting rod 13 is arranged inside of a propeller shaft 6 so as to be extended, exceeding both ends thereof. An end of the adjusting rod 13 is connected to the adjusting mechanism 10, and a radial flange 14 is provided, and the radial flange is supported by a thrust bearing 15. The thrust bearing 15 is arranged inside of the hollow piston 16, and a cylinder 17 for storing the hollow piston is inserted into a casing 1. With this structure, structure length to be required for thrust bearing becomes unnecessary, and the hydraulic oil or the lubricating oil is supplied to the thrust bearing for lubrication and cooling through the lubricating oil supplying passage or the lubricating oil supplying hole on the basis of a pressure difference between a rotating part and a fixed part.