PURPOSE: To enable the efficient execution of the orthosis of a bad posture, such as rounded back or stoop, by constituting the underwear of a pelvis covering belt formed to a band shape, a jacket provided with a pair of cup parts and a back rest connecting the belt and the jacket.

CONSTITUTION: The underwear 1 for backbone orthosis is constituted of the pelvis covering belt 2 formed to the band shape, the jacket 3 and the back rest part 4 connecting the belt and the jacket. The pelvis covering belt 2 is wound around the pelvis of the body and is freely disengageably engaged at an arbitrary point at the time of wearing. The back rest part 4 is connected to an outer connecting piece 23b and inner connecting piece 23a extending from the pelvis covering belt 2. Further, an orthosis piece 24 is stitched to the surfaces of the outer connecting piece 23b and the back part 21, by which the front end 24a of the orthosis piece 24 and the surfaces of left and right front surface parts 22 are freely disengageably engaged at an arbitrary point. The jacket 3 is formed of a front body 31 and a rear body 32. A pair of the cup parts are provided on the front boy 31. The rear body 32 is inserted into the spacing between the inner and outer connecting pieces 32a, 32b extended from the pelvis covering belt 2.