PURPOSE: To perform high quality bar code printing, by a method wherein a bar code reading function is added to a printer having a bar code printing function to check a printed bar code and overlap-printing is performed when an error is detected to correct the error.

CONSTITUTION: A printer control part 6 drives a printing head 4 on the basis of the bar code data sent from a host and a bar code 3 is printed on paper 2. After the finish of printing, a bar code sensor 5 reads the printed bar code 3 to apply a bar code signal to a bar code check circuit 7. The bar code check circuit 7 checks the rightfulness of the inputted bar code signal and, when an error is detected, the error is informed to the printer control part 6. The printer control part 6 receives the information of the error to inform the error to the host and the same bar code is printed on the bar code printed previously in an overlapped state by the indication of said host.