To solve the problem of determining opening of a valve seat in a position of a water surface via a float, due to being constituted so that magnetic force attenuates in inverse proportion to a square of a distance when separating even a little and a rubber valve seat also integrally operates in response to the float, though strong magnetic force is generated when attracted, in a drain trap of using a direct magnetic force system for generating attraction force by directly attracting a conventional magnet and a mating member.

A permanent magnet 23 is rocked in response to rocking of the float 20 by a quantity of drain water gathered in a cover 10, and the drain water is intermittently drained by opening the valve seat 51 connected to a drain port 10b by the movement by attraction of a valve element 52 by indirect magnetic force for making the magnetic force act by putting a space or an object or its both between the permanent magnet 23 and the valve element 52 of a normal magnetic substance being an attraction object.