PURPOSE: To improve the draining performance of a case for defrosted water drainage wherein float is contained by providing a hole opposed to a drain port at the bottom of the case, forming a water flow channel at the entire lower surface, and providing the float for blocking the port via a hole and an operating member for lifting the case in a low-temperature box.

CONSTITUTION: A drain port 21 for draining defrosted water of cooling means contained in a cooling chamber 8 is provided at the bottom of a case 24. A hole 28 opposed to the port 21 is provided at the bottom. A cutout 27A and a through hole 27B are formed at the entire lower surface. A float 23 for blocking the port 21 and an operating member 26 for lifting the case 24 are contained in the case 24. Thus, the draining performance of defrosted water when the float 23 is contained in the case 24 can be improved.