To provide a boring machining device which can easily form a supply path of a liquid, easily adjust the pressure of the liquid supplied to each hydrostatic pressure pocket, and improve a machining precision of a workpiece.

A small diameter shaft part 23c of a rotary rod 23 is inserted in an inner part of a cylindrical support hole 31a of a bush 31 composing a second bearing part 26. First to third hydrostatic pressure pockets 32a to 32c are formed in the cylindrical support hole 31a, first to third pressure regulating valves 36a to 36c are connected to the first and third supply tubes 35a to 35c, and the pressure of the oil supplied to the first to third hydrostatic pressure pockets 32a to 32c is regulated. The bores to be machined of a cylinder head is machined with a tool provided on the rod 23 while supporting the rotary rod 23 by an appropriate hydrostatic pressure liquid bearing by adjusting the respective pressure in the hydraulic pressure pockets 32a to 32c, and correcting so that the axis line O1 of the rotary rod 23 becomes coaxial to the axis line O2 of the cylindrical support hole 31a of the bush 31.

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