An optical code reading process and a reading stability determining process are performed while suppressing an increase in the cost of a transfer system and avoiding a decrease in work efficiency. CCD performs imaging. Processor reads a one-dimensional code contained in image data taken by CCD, and outputs a signal when a reading process in which the number of reading successes related to the one-dimensional code reaches a determination reference value is completed. In addition, processor determines reading stability during a period from the first reading success to completion of the reading process and outputs predictive maintenance information (PMI) representing a determination result of reading stability.