To incorporate the power source for driving a bar code reader into the reader unit consisting of a bar code reader and a connector for interface.

In this unit consisting of a bar code reader 5 reading the bar code imparted to an article and a connector 24 for interface connecting this bar code reader 5 and a main body CPU 3, a power source circuits 20 (21) detecting a signal from at least one or more input/output pins, converting this detected current into DC voltage and current and using the voltage and current as a current source is made to be incorporated into the bar code reader 5 or the power source circuit is incorporated into the bar code reader 5 on into a connector 24 for interface in place of the bar code reader 5. Thus, the bar code reader 5 is not required to be connected to an external power source. Also the shape and structure of the bar code reader 5 itself is not entirely different from a conventional bar code reader. Further, the bar code reader is not required to have the power source box that the conventional bar code reader has and the number of parts for the box is reduced.