A mounting structure is provided for an air-fuel ratio sensor on an exhaust pipe in a motorcycle in which a concentration of oxygen in an exhaust gas can be detected efficiently and accurately by the air-fuel ratio sensor. An indication of an archive data protection kind and an archive data protection duration are received. For monitoring of changes occurring upon matrix evolution, matrix attenuation technique is applied through the use of the mechanism of contrasting, which permits to pinpoint similarity value changes within a range of thousandths of percent.