To provide a free float drain trap to be able to remove a valve seat member without disassembling a valve casing.

The valve casing is comprised of a main body 1 and a lid 2. An inlet 5, a valve chamber 4, and an outlet 7 are formed in the valve casing. The valve chamber 4 side end 4 of a valve seat member 9 having a discharge passage 8 communicating with the valve seat 4 at the outlet 7 side is projected into the valve seat 4, and detachably mounted to the lid 2. A spherical float 12 is disposed in the valve chamber 4 in a free state to open and close the discharge passage 8 by directly seating and unseating the valve chamber 4 side end of the valve seat member 9. Two partially cylindrical float seats 13 having a radius which is a little greater than the float 12 coaxially with the discharge passage 8 are formed parallel to each other in the axial direction. An annular auxiliary valve seat 11 is formed in the outer periphery of the valve chamber 4 side projection portion of the valve seat member 9 projecting into the valve chamber 4. The valve chamber 4 side end of the annular auxiliary valve seat 11 is positioned in the rear of the valve chamber 4 side end of the valve seat member 9.