PROBLEM TO BE SOLVED: To improve dispersivity of a magnetic particle bonded to a biological constituent substance in a solution by demagnetizing residual magnetization of the magnetic particle attracted and captured by magnetic attraction force by use of an alternating magnetic field. SOLUTION: When demagnetizing a magnetic body, the alternating magnetic field is applied to the magnetic body, and intensity of the alternating magnetic field is gradually reduced to zero. Thereby, an area of a magnetization-magnetic field hysteresis curve (a B-H curve) of the magnetic body is reduced while the hysteresis curve draws hysteresis, finally an operation point thereof reaches a point of magnetization (B) = 0, a magnetic field (H) = 0 that is the origin of the hysteresis curve, and the magnetic body is demagnetized. COPYRIGHT: (C)2005,JPO&NCIPI
