PURPOSE: To provide a lost foam pattern casting method for casting pipe with a branched pipe causing no projecting casting defect in the branched pipe part.

CONSTITUTION: The lost foam pattern formed of a foamable synthetic resin having the branched pipe part 2 opened in axial direction of a main pipe part 1 is embedded into dry sand 6 in a molding flask 5 so that the opening part of the branched pipe part 2 directs downward to constitute a mold. Then the opening part of the branched pipe part 2 in the lost foam pattern is closed beforehand with the seat-like member 4. Further, by pouring molten metal into the lost foam pattern, the pattern is burnt and gasified, and also the molten metal is cast into a casting cavity formed by losing the pattern.