DRAIN TRAP

Provided is a drain trap that allows easy maintenance, yet has high durability with ability to prevent condensation. The drain trap includes a bottomed cylindrical main body portion 5 having a lateral wall 51 on which a receiving pipe portion 2 for receiving liquid and a discharge pipe portion 3 for discharging the liquid are formed, an attachable/detachable partitioning body 1 for partitioning an inside space 4 of the main body portion 5 into a reservoir space 7 and a discharge space 8, a lid portion 6 for closing the inside space 4 of the main body portion 5 and a sealing case 9 surrounding, under a sealed state, at least a portion of an outer surface of the main body portion 5 in which the reservoir space 7 is formed. An air gap 91 is formed between the sealing case 9 and the main body portion 5. The sealing case 9 and the main body portion 5 are formed transparent. The lid portion 6 is attachable/detachable when the sealing case 9 is attached to the main body portion 5.