Bar-code reader and method of reading bar-code

A bar-code reader that scans a bar code that is formed by black bars and white bars each having a width that is an integral multiple of a basic width, comprising:

• a differential processing unit that calculates differential of a signal obtained by optically scanning the bar code to thereby obtain a differential data;
• a peak detector that detects peaks in the differential data;
• a peak-to-peak distance calculating unit that calculates peak-to-peak distances for all the peaks detected, the peak-to-peak distance being a distance between two adjacent peaks;
• a frequency-mapping unit that calculates, for each of the peak-to-peak distances, candidate values for the basic width by dividing the corresponding one of the peak-to-peak distance by each of a plurality of integral numbers that are possible candidates for the integral numbers respectively;
• a transition-route forming unit that selects, based on a predetermined criteria, a candidate value for the basic width corresponding to each of the peak-to-peak distances to thereby form a combination pattern for each candidate values of the basic width;
• and
• an error judging unit that judges an mount of error in each of the combination patterns, and determines a combination pattern, as a candidate combination pattern, having least amount of error from among the combination patterns;
• a basic-width determining unit that calculates the basic width from the candidate values for the basic width in the candidate combination pattern.