To manage a drainage unit hygienically while enhancing heat insulation.

The trap 10 of a drainage unit 9 comprises an inlet pipe 10A interconnected with a storage compartment 4, a pipe 10B directed upward from the lower part of the inlet pipe 10A, and an outlet pipe 10C led out downward from the upper part of the upward pipe 10B, wherein a hole 12 is made at the lower end of the inlet pipe 10A and fixed with a plug 13 removably.