PROBLEM TO BE SOLVED: To provide an orthosis capable of easily adjusting circumference length and aligning the joint or the trunk normally.SOLUTION: The orthosis comprises a fixing member, a belt-like member disposed inside the fixing member for surrounding a region of a living body, and an adjustment member fixed to the fixing member. The adjustment member includes a rotating body having a first engagement part, and an extrusion body having a second engagement part to be engaged with the first engagement part. At least one of the first engagement part and the second engagement part is a screw thread. With the rotation of the rotating body, the extrusion body moves in the axial direction of the rotation, and the extrusion part presses an external face of the belt-like member.
