A bar code reader includes bar code processing units (10, 11) for generating a bright/dark pattern forming a bar code (40) by optically scanning a bar code forming surface of an object (4), converting into plural categories of module values indicating widths of the respective areas, and demodulating the bar code into character data, a scaling unit for creating scale data by scaling a weight of the object to be sold by weight, a adjustment control unit (11) to perform zero-setting in response to a request for initializing the scaling unit, and a weight change detecting unit (11) for judging at least one of an increment change and a decrement change from zero in weight, and making a corresponding piece of scale data visibly displayed when in the increment change and making an absolute value of a corresponding piece of scale data visibly displayed when in the decrement change.