The faceting and the shrinkage processes of ridge structure fabricated along [1 1 0] on GaAs (0 0 1) substrate with As-2 flux and As-4 flux were monitored by microprobe reflection high-energy electron diffraction/scanning electron microscopy (microprobe-RHEED/SEM) installed in the MBE chamber. It was found that the shrinkage of top size with As-4 flux was faster than that with As-2 flux. To analyze the result of the experiments, the calculation based on two-face inter-surface diffusion model was conducted. From this calculation, we show that the shrinkage of the top size is slower when the arsenic pressure is higher, simply because the lateral flow of Ga adatoms towards the top surface becomes smaller. Under the As-2 flux, the amount of Ga adatoms which migrate to (0 0 1) surfaces from (1 1 1)B surface becomes smaller compared with that under As-4 flux due to the higher reactivity of As-2 to Ga adatoms.