The universal product code consisting of black bars and white spaces carrying information is discriminated by counting the occurrence period of electric signals corresponding to the guard pattern and averaging the count obtained thereby to provide a width information of the basic module, discriminating the first character by sampling the code in stop-start synchronization based on the width information, counting the occurrence period of electric signals corresponding to the (n-1)th character to provide another width information of the basic module from the count obtained thereby, and discriminating the n-th character by sampling the code in stop-start synchronization based on the basic module. Therefore, a high performance code discriminator can be achieved by a simple structure.