To provide a ceiling mounting structure of a bathroom unit capable of ensuring all of workability, architectural design property and space saving nature.

A ceiling panel mounting device has such a structure that a groove for fitting the side end of a ceiling panel projecting an insertion guide piece from an upper surface and projectively forming the first connecting section in a lower surface is formed, at the same time, the second connecting section corresponding to the first connecting section formed into the ceiling panel mounting device is formed in the upper end of a wall panel and that a joint section wherein the first connecting section and the second connecting section are mutually pressed is provided.