PURPOSE: To swiftly mix solutions and to easily exchange samples by providing a magnetic attraction means which vertically moves the agitation piece laid in the upper part of the vessel receiving sample liquid, and a revolving magnetic field mechanism rotating the agitation piece.

CONSTITUTION: The revolving magnetic field mechanism 2, 3 is provided under the holding body 4 holding the vessel S receiving the sample liquids, and the magnetic attraction means 5 which horizontally generates the magnetic line of force with the bessel S between is provided to be vertically movable. A 1st liquid to be reacted is received in the vessel S and a 2nd liquid in the rotation piece 10 and the rotation piece is set in the upper part of the vessel S. Then, the rotation piece 10 is lowered while being revolved by the magnetic attraction means 5 and the revolving magnetic field mechanism 2, 3, so that the two liquids are swiftly mixed. The exchange of samples is easily carried out by exchanging the vessel.