A magnetic separator comprising: a conveyer belt of a second belt conveyer to carry a powder and granular material (a) containing ferromagnetic particles: a rotatable hollow belt guide roll having an outer circumference partly wound with the above-described conveyer belt; and a magnetic field application device disposed inside the belt guide roll, a first belt conveyer to carry the powder and granular material (a) containing ferromagnetic particles; and the second belt conveyer provided with the magnetic field application device and located above the first belt conveyer, and wherein the magnetic field application device includes a plurality of magnets inside the belt guide roll, the magnets are arranged in such a way that magnetic poles adjacent in the circumferential direction of the belt guide roll are different from each other, the powder and granular material (a) containing ferromagnetic particles is supplied to the first belt conveyer from a supply device, a conveyer start edge portion of the second belt conveyer is closely located above a conveyer end edge portion of the first belt conveyer, and a magnetically attracted material recovery portion is disposed below the conveyer end edge portion of the second belt conveyer and a magnetically not-attracted material recovery portion is disposed below the conveyer start edge portion of the second belt conveyer, and wherein the conveyer start edge portion of the second belt conveyer is a portion in which the powder and granular material (a) containing ferromagnetic particles starts to contact with the second belt conveyer and the conveyer end edge portion of the second belt conveyer is a portion in which the powder and granular material (a) containing ferromagnetic particles is discharged from the second belt conveyer, wherein the conveyer end edge portion of the first belt conveyer is a portion where the powder and granular material (a) slips between the conveyer end edge portion of the first belt conveyer and the conveyer start edge portion of the second belt conveyer, and wherein the magnetic field change frequency F in Hz, which is defined by the following formula and which indicates changes in the magnetic field acted on the powder and granular material (a) from the magnetic field application device, is 170 Hz or more, F = x ⋅ P / 60 where x: the number of revolutions per minute of a magnet roll P: the number of magnetic poles provided to the magnet roll, wherein, as for the number of magnetic poles, a pair of the north pole and the south pole adjacent in the circumferential direction of the surface facing the powder and granular material (a) of the magnet roll is counted as one magnetic pole. a rotatable hollow belt guide roll having an outer circumference partly wound with the above-described conveyer belt; and a magnetic field application device disposed inside the belt guide roll, a first belt conveyer to carry the powder and granular material (a) containing ferromagnetic particles; and the second belt conveyer provided with the magnetic field application device and located above the first belt conveyer, and wherein the magnetic field application device includes a plurality of magnets inside the belt guide roll, the magnets are arranged in such a way that magnetic poles adjacent in the circumferential direction of the belt guide roll are different from each other, the powder and granular material (a) containing ferromagnetic particles is supplied to the first belt conveyer from a supply device, a conveyer start edge portion of the second belt conveyer is closely located above a conveyer end edge portion of the first belt conveyer, and a magnetically attracted material recovery portion is disposed below the conveyer end edge portion of the second belt conveyer and a magnetically not-attracted material recovery portion is disposed below the conveyer start edge portion of the second belt conveyer, and wherein the conveyer start edge portion of the second belt conveyer is a portion in which the powder and granular material (a) containing ferromagnetic particles starts to contact with the second belt conveyer and the conveyer end edge portion of the second belt conveyer is a portion in which the powder and granular material (a) containing ferromagnetic particles is discharged from the second belt conveyer, wherein the conveyer end edge portion of the first belt conveyer is a portion where the powder and granular material (a) slips between the conveyer end edge portion of the first belt conveyer and the conveyer start edge portion of the second belt conveyer, and wherein the magnetic field change frequency F in Hz, which is defined by the following formula and which indicates changes in the magnetic field acted on the powder and granular material (a) from the magnetic field application device, is 170 Hz or more, F = x ⋅ P / 60 where x: the number of revolutions per minute of a magnet roll P: the number of magnetic poles provided to the magnet roll, wherein, as for the number of magnetic poles, a pair of the north pole and the south pole adjacent in the circumferential direction of the surface facing the powder and granular material (a) of the magnet roll is counted as one magnetic pole.