To enable a page marking to be accurately detected even when the page marking is displaced forward by not less than a half of the clearance between the bars, thereby improving the page marking detection performance.

The passbook entry machine sets areas where respective bars corresponding to page markings comprised of multiple bars are searched, starts the searching with the searching area of the bar on the posterior end side based on the data obtained from the output to the CCD licenser 8 which reads the page markings, and stores in the storage the bit data worth of the number of bars which show whether or not the detection has been made for every bar. If the rear end bar is not detected, the passbook entry machine sets one bar's worth of a searching area on the anterior side to the searching area of the leading bar and conducts the searching in the area. In case the bar is detected by this searching, the value after the bit data of the bar is added to the bit data as the highest-order bit and is displaced to the lower-order side by one bit is regarded as the detection result of the page marking.