In tandem mirror GAMMA 10/PDX, H2 gas has been injected to a divertor simulation experimental module (D-module) for radiation cooling and detachment study. Electron temperature (Te) and density (ne) distributions have been measured by Langmuir probes in the D-module. With increase of H2 gas amount, Te has decreased especially at the V-shaped target plate from 30-40 eV to 3-5 eV. Moreover, ne and ion saturation current Iis have increased at the inlet but decreased at the target and had a steeper distribution toward the corner. These results suggest detachment. The movement of the ionization front to the upstream side with increase of the gas is suggested from the change in the plasma parameters profiles along the magnetic field line.