A balancer, comprising a weight (4) held by a weight holder (3) having a pressing surface (4b') pressed against a guide surface (12a) provided on the weight holder (3) in the rotating circumferential direction by a centrifugal force by the rotation of a rotating body, wherein the weight (4) pressed against the guide surface (12a) through the pressing surface (4b') during the rotation of the rotating body is disposed at a position for suppressing the swing of the rotating body by varying the position thereof in the rotating circumferential direction relative to the rotating body, the guide surface (12a) and the pressing surface (4b') are tilted relative to a rotating axis direction divergently toward one end of the rotating body along the rotating axis, and the weight (4) is pressed against a support part (7a') by the components of the centrifugal force along the guide surface (12a) and the pressing surface (4b').