According to an embodiment of the present disclosure, a water detector of a double structure with a freeze protection function is disclosed. The water detector includes: an external body including a container-shaped structure which has an empty space formed therein, and includes a side surface portion, an upper portion, and a lower portion; and an internal body which is inserted into an inside of the external body and coupled thereto, the internal body including a container-shaped structure which has an empty space formed therein, and includes a side surface portion, an upper portion, and a lower portion.