We construct a new detector to monitor $\gamma$ yields in bunch by bunch
basis for the Laser Compton experiment at the KEK ATF which is capable to
separate $\gamma$ rays in 5.6ns-spacing multi-bunch operation of the KEK ATF.
In this article we report a result of measurement of multi bunch $\gamma$ ray
detection for the first time at the KEK ATF.Comment: 6 pagese 4 figures, Proceedings of POSIPOL 2011, Beijing Aug. 201