To provide a balancer wherein the balancing force can be adjusted in the state of a single body without being fit to a double-hung window.

The balancer comprises a cylinder 10, a torsional spring 11, a rotational body 12, and a spiral rod 13. When the spiral rod 13 is moved in the longitudinal direction of the cylinder 10, the rotational body 12 is rotated. By the rotation of the rotational body 12, the torsional spring 11 is wound/unwound, and at the same time the rotational body 12 is rotated together with the spiral rod 13. A balancer includes a movable member 14 connected to the spiral rod 13, and the lower end 10c of the periphery 10b of the cylinder 10 and a recess 14a of the movable member 14 are fit to each other so as not to rotate relatively. The balancing force can be adjusted in the following way, that is, in the state in which the torsional spring 11 is wound up by rotating unidirectionally the spiral rod 13 together with the movable member 14, the cylinder 10 and the movable member 14 are fit to each other, the movable member 14 and the cylinder 10 are held so as not to relatively rotate by fitting as stated above the cylinder 10 and the movable member 14 to each other.