To allow displacement between a usable condition and an unusable condition without removing a headrest by arranging a neck support movably between a protruded position, in which it is protruded from a backrest front face, and a retracted position, in which it is not protruded from the backrest front face, and arranging a holding means holding the neck support in the protruded/retracted position.

A neck support 7 is arranged between a backrest 1 and a headrest 4. The neck part support 7 is divided laterally in the center into two split bodies 8, 9. Shafts 5, 6 of the headrest 4 are respectively passed through the split bodies 8, 9, which can be turned around the shafts 5, 6 individually. Insertion holes 10, 11 in the split bodies 8, 9 are formed while biased to their rear parts. In this way, when the both split bodies 8, 9 are connected forward to each other in parallel, their front faces 8a, 9a are protruded from an upper front face 1a of the backrest 1, so that the neck support 7 can be used. When the both split bodies 8, 9 are turned so as to be arranged backward, the neck support 7 is set in an unusable condition.