In order to test the mechanical/thermal stability of the BPM mounted on the magnet, we did a set of bench test with the prototype BPM. A mechanical stress was applied on the BPM chamber directly or through a bellows monitoring the position change of the BPM with respect to the magnet. The displacement was proved to be less than a few micron. The stability of xy-isolation of the BPM was also tested under the mechanical stress. No significant change was seen.