Progress of etching of diamond (100) surface by atomic hydrogen was observed in real time with the help of reflection high energy reflection diffraction. The initial 1x1 pattern that indicates smooth two dimensional extension of the crystal surface transformed into the pattern corresponding to the (110) reciprocal lattice plane that indicates surface roughening. Ex situ atomic force microscope observation of the etched surface revealed a lot of shallow etch pits with a few nm in depth and a few degrees in the slope of the pit. It is supposed that deposition is effective against etching in actual chemical vapor deposition conditions partially because of the difference in their favorable temperatures, in addition to the absolute difference in their rates.