Drain trap

To provide a drain trap which makes it possible to easily clean the interior of a main body and accurately seal a junction between storage space and discharge space partitioned by a partition. The drain trap includes the main body which has a tubular shape with a closed end and includes inner space communicated with a receiving unit and a discharge unit; a lid; and the partition which partitions the inner space of the main body into the storage space and discharge space, in which the partition can be inserted into the inner space, sealing units are installed on the partition and a side wall of the main body to bring part of the partition into intimate contact with part of the side all by exerting a vertical force component under a vertical pressing force, and the partition is equipped with a valve disc which floats up to allow liquid to flow from the storage space to the discharge space when the liquid in the storage space reaches or exceeds a set amount as well as with a valve seat which catches and supports the valve disc.