An automatic analyzer includes a B/F separator including a reaction vessel holding unit provided with magnets disposed around a reaction vessel held on the reaction vessel holding unit and a rotating device for rotating the reaction vessel holding unit holding the reaction vessel about an axis of rotation aligned with the center axis of the reaction vessel or an axis of rotation parallel to and separated by a distance from the center axis of the reaction vessel. Both magnetic force and centrifugal force are exerted simultaneously on a specimen contained in a reaction vessel to capture magnetic particles contained in the liquid contained in the reaction vessel at a high capturing efficiency.