A mandrel for bending which inhibits generation of irregularities on the inside of the bend is provided. The mandrel comprises a plurality of plugs in the form of discs and a through-hole is created substantially in the center of each plug. A flexible member is inserted through the through-holes of the respective plugs. One end of the flexible member is fixed to a shank so that the plugs are connected to the shank in series. Each plug is provided with a flat slant surface that descends from about the center of the plug toward the outer periphery of the plug. A lock hole is formed in parallel to the through hole in each plug and a flexible lock member, one end of which is fixed to the shank, is passed through the lock holes of the respective plugs.