There are many ways to paint Hanshan and Shide (J: Kanzan and Jitoku), and this study will focus on a specific type, in which the two persons are shown as looking up or pointing up with fingers. The meaning of this type of painting often remains unexplained in modern studies, or is vaguely described as containing some message of Zen. This study, however, will prove that both Chinese and Japanese monks understood that Hanshan and Shide were looking at the moon even though nothing was painted on the paper or silk.This study probes into the issue of how Zen monks interpreted paintings. They did not limit themselves to the images painted, but they did not develop their imagination completely freely. This paper, based on inscriptions and records of monks, demonstrates that Zen monks showed their personal expression with mutual understanding. In this case, they were all familiar with a poem written by Hanshan, even though the contents were not clearly illustrated in the paintings. This paper also argues that Japanese Zen paintings were not similar to the Chinese prototypes only in forms; instead, Japanese viewers fully understood the context with which Chinese monks interpreted paintings.