A new radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) method, named droplet elimination by radical beam irradiation (DERI), is utilized for the growth of InN. This method is composed of two series of growth processes: (1) InN growth under an In-rich condition and (2) consecutive nitrogen radical beam irradiation. This method is simple, enabling the reproducible growth of a high-quality thick InN film with a flat surface. This method is also effective for monitoring a nitrogen radical beam that is responsible for InN growth. This new growth method is also applied to InGaN growth. The results indicate a preferable Ga capturing process on an InGaN growing surface, particularly when the samples are grown under a metal-rich condition.