To provide a method and an apparatus for cutting an inner surface bead of a welded tube capable of consistently cutting the inner surface bead of the welded tube even when the wall thickness of the welded tube is changed during the cutting.

An inner surface bead is cut by pressing a cutting tool 14 attached to a mandrel 13 inserted with a space in the welded tube to be conveyed in the axial direction by a pair of upper and lower drive rolls 12 rotated while being abutted on an outer surface with the inner surface bead being located on a lower part against the inner surface bead on the downstream side of the conveying direction of the welded tube from the abutting position of the pair of upper and lower drive rolls 12. Based on the thickness of bead chips to be cut and discharged by the cutting tool 14, the pair of upper and lower drive rolls 12 apply the upward or downward external force to the welded tube at a part on the downstream side of the conveying direction of the welded tube from the abutting positions of the pair of upper and lower drive rolls 12, and the welded tube is elastically deformed to adjust the cutting amount of the inner surface bead by the cutting tool 14.