1. A stack barcode reader for use with a stack barcode in which information is encoded so as to be expressed with a bar and a space, the stack barcode reader comprising: an imaging unit for imaging the stack barcode; an image memory for storing an image datum of the stack barcode imaged by the imaging unit; and a data processing unit comprising a decoding unit for decoding an encoded information expressed as the stack barcode, on the basis of the image datum; wherein, the decoding unit comprises: a line width measurement means for measuring width of a bar and a space of the stack barcode, on the basis of a plurality of pixel values constituting the image datum; a T-sequence measurement means for measuring a T-sequence, being a sequence of numerical values, according to line width of a bar and a space of the stack barcode measured by the line width measurement means; a code-word obtainment means for obtaining a code-word corresponding to the T-sequence at least measured by the T-sequence measurement means; and a T-sequence modification means that compares a cluster value obtained from the T-sequence by the T-sequence measurement means, with a theoretical cluster value, and modifies the T-sequence by using the theoretical cluster value and the conversion table of T-sequence/code-word if there appears a difference between the two cluster values.