To provide a back straightener allowing even a person with weak grip, such as a senior person and a woman, to readily straighten his/her back without putting a burden on the body.

In the back straightener, two armpit portions (horizontally moved, rotatable) which are held under the armpits of both arms of the user seated on a chair and from which the user hangs down, are provided from the back side, and the chair being vertically adjusted is provided at a place under the armpit portions. The armpit portions are held under the armpits of both arms of the user, the user is seated in the chair and hangs down from the armpit portions. The chair is adjusted to be stopped immediately before making a space between the chair and the buttocks of the user or to make a space between the chair and the buttocks, so that the body weight put on both armpits are adjusted, and the user is allowed to hang down while the back of the user is straightened without a burden on the body.