POSITION TRACER

PURPOSE:To make any damage to be produced at the time of changing preventable, by supporting a part holding device shiftably in three-dimensional directions in a static pressure manner, while installing a discharge part which discharges a medium, statically holding the part holding device, via a throttle. CONSTITUTION:Pressurized gas is fed to an air pocket 3 of an air chamber 2 from a tube 6 via a nozzle 5. If so, a thrust plate becomes floated so that it is smoothly movable to external force in the horizontal direction. If so, in the case where there is dislocation between an assembling part 13 and an assembled part 14, if reaction between parts at a chamber to be produced by a descent of the assembling part 13 acts thereon even slightly, the assembling part 13 is made traceable so as to fit with the assembled part 14. Here, such force in the horizontal direction as necessary to trace so as to absorb the dislocation is influenced by a flow rate to be discharged out of an air port 7 of a throttle 8.