Experiments showed that a generation of wear elements, that means elemental debris of wear particles, induced a spontaneous magnetization of the sliding surface (i.e. tribomagnetization phenomenon) when the ferromagnetic materials iron, nickel and cobalt were subjected to sliding friction in the absence of an external magnetic field. Origin of the tribomagnetization phenomenon that arose through the generation of wear elements with a size of about 15nm to a few tens of nanometer, a size that was of the same order as that of a single magnetic domain particle of ferromagnetic materials, was revealed by using a magnetic force microscope (MFM). The magnetic flux density that varied in both strength and direction over the entire sliding surface was identified by using a Tesla meter with a three-axis or single-axis probe. From experimental results the relation between a generation of wear elements in tribological process and the original process in mechanism of the tribomagnetization phenomenon was discussed.