A device for separating weakly magnetic first particles, for example hematite particles, from mixture (912) comprising the first particles (913) and less magnetic second particles (914) is presented. The device comprises first magnetizing equipment (901) for producing magnetic field and for moving the mixture so that mutually opposite polarity portions (N, S) of the magnetic field sweep the mixture in a sweeping direction and thereby deflect the direction of movement of the first particles towards the sweeping direction and away from the direction of movement of the second particles. The device comprises also a supply equipment (932) for supplying the mixture to the carrier equipment with the aid of gravitation and a second magnetizing equipment (931) connected to a feed box (920) for producing second magnetic field for deflecting a direction of movement of the first particles differently than a direction of movement of the second particles when the mixture is moved by the gravitation towards the carrier equipment so as to generate, to the mixture arriving at the carrier equipment, a concentration gradient of the first particles. The pre-concentration of the first particles simplifies their separation form the mixture.