  We are developing a new photon detector with micro pattern gaseous detectors.
A semitransparent CsI photocathode is combined with 10cm$\times$10cm
GEM/$\mu$PIC for the first prototype which is aimed for the large liquid Xe
detectors. Using Ar+C$_2$H$_6$ (10%) gas, we achieved the gas gain of $10^5$
which is enough to detect single photoelectron. We, then, irradiated UV photons
from a newly developed solid scintillator, LaF$_3$(Nd), to the detector and
successfully detected single photoelectron.
