Abstract: A bent product having a three-dimensionally bent portion intermittently or continuously in the lengthwise direction is manufactured by supporting a steel pipe at a first position A while feeding it in the lengthwise direction, locally heating the steel pipe being fed at a second position B, cooling the heated portion of the steel pipe at a third position C, and varying the position of a gripping means, which grips the steel pipe in a region ID downstream of the third position C, in a three-dimensional direction including the feed direction of the steel pipe in a workspace including a space on the upstream side of the third position C in the feed direction of the steel pipe to impart a bending moment to the heated portion of the steel pipe.