We have studied the beam orbit tilt monitor for stabilizing the beam orbit in ATF2 as well as future international linear collider. Once we can measure a beam orbit tilt with high precision at one point, we can relate this data with the beam position profile at the focal point. Tilt monitor is a new type of the cavity beam monitor, like cav BPM. According to our simulation, the expected limitation is about 35 nrad. The prototype was completed and installed in the test area on the ATF2 beamline. The first beam test have been done in December 2009.