The oil separator 11 separates oil in the refrigerant discharged from the compressor 4 and returns the oil back to the compressor 4. And includes a tank 21 into which refrigerant discharged from the compressor 4 flows, a float 24 whose inside is hollow formed by welding a plurality of members and made vertically movable according to the changes in the oil surface 20 inside the tank 21, and a needle valve 29 that returns oil inside the tank 21 to the compressor 4 according to the vertical movement of the float 24. The float 24 is provided such that the end point 24E of the welded portion comes above the oil surface 20.