The present invention provides a method and an apparatus capable of continuously and accurately separating, by type, a mixture containing at least two types of particles, or capable of separating specific particles from the mixture, using a gradient magnetic field. In the present invention, a mixture containing at least two types of particles, particles of one type of which are made of a paramagnetic or diamagnetic substance, is treated. A magnetic field whose magnetic field gradient has a vertical component and a horizontal component is applied to a supporting liquid 21 stored in a separating tank 31. When the mixture is placed into the supporting liquid 21, the particles of the one type are guided such that they are positioned in the supporting liquid 21 at a predetermined height from a bottom face 39 of the separating tank 31 while horizontally traveling. Alternatively, the particles of the one type magnetically levitate at a liquid surface of the supporting liquid 21 and horizontally travel. Particles of another type of the at least two types of particles are positioned at a position vertically different from that of the particles of the one type, between the bottom face 39 of the separating tank 31 and the liquid surface of the supporting liquid 21.