An apparatus for bending a glass tube to a U shape having a pair of chucks for holding the glass tube at both sides, a heating device for heating and softening the glass tube held by the chucks at the predetermined zone for bending, and a turning mechanism for the chucks. The turning centers of the turning mechanism are set each at positions located at a predetermined distance inwardly from an axis of the unbent glass tube held by the chucks. The distance between the turning centers is less than the distance between the axes of straight zones of the glass tube formed after bending. There is also a bending drum for guiding bending, which drum moves forwardly and backwardly into and away from the predetermined zone for bending of the glass tube.