Abstract: A first portion of a perimeter of an outer circumferential portion of a tire is magnetized with a first polarity along the steel belt in one circumferential direction less than 360° and a second portion of the perimeter is magnetized with a second polarity in an opposite circumferential direction. The magnetic field generated by the magnetized steel belt is detected by two magnetic detection elements, which are set so that the magnetic field detection directions of the two magnetic detection elements are parallel to the side surface of the tire, and the two elements are juxtaposed in a direction perpendicular to the side surface of the tire.

Abstract: A tire (12) used includes a steel belt in its outer circumferential portion. A magnetic sensor (14) including a pair of magnetic detection elements (18A, 18B), which are arranged so that their magnetic detection directions become parallel to each other or series each other, is set in the vicinity of a rear tire (12) in a trunk room of a vehicle (10). Changes in magnetic field upon revolution of the tire (12) are differentially detected by the magnetic detection elements (18A, 18B), and the revolution of the tire (12) is detected on the basis of the differentially detected output waveform. Among a plurality of peaks present in the differentially detected output waveform, a peak, the potential difference from the immediately preceding peak of which is equal to or larger than a predetermined threshold value, is detected as an effective peak, which is effective for tire revolution detection, and the revolution speed of the tire is calculated by detecting the number of effective peaks.

Abstract: A tire (12) used includes a steel belt in its outer circumferential portion. A magnetic sensor (14) including a pair of magnetic detection elements (18A, 18B), which are arranged so that their magnetic detection directions become parallel to each other or series each other, is set in the vicinity of a rear tire (12) in a trunk room of a vehicle (10). Changes in magnetic field upon revolution of the tire (12) are differentially detected by the magnetic detection elements (18A, 18B), and the revolution of the tire (12) is detected on the basis of the differentially detected output waveform. Among a plurality of peaks present in the differentially detected output waveform, a peak, the potential difference from the immediately preceding peak of which is equal to or larger than a predetermined threshold value, is detected as an effective peak, which is effective for tire revolution detection, and the revolution speed of the tire is calculated by detecting the number of effective peaks.

Abstract: A magnetization magnet (11) is brought into contact with or close to the outer circumferential surface of a tire (12) that has a steel belt in its outer circumferential portion, and is relatively moved along the circumferential direction of the tire (12) so that the magnetic field generated by the magnetization magnet (11) runs in the circumferential direction of the tire. (12), thereby magnetizing the tire (12). The entire perimeter of the outer circumferential portion of the tire (12) is continuously magnetized in one direction along the circumferential direction. After the polarities of the magnetization magnet (11) are inverted with respect to the circumferential direction of the tire (12), an angle range smaller than 360.degree. on the outer circumferential portion of the tire is continuously re-magnetized in a direction opposite to the one direction.