A micro-controller integrated on a single substrate and which includes a read-only information memory for storing firmware, an address controller for performing address control, and an input port for inputting information supplied thereto from a source external to the substrate further incorporates a correcting information storage memory for receiving correcting information input thereto from the source external to the substrate through the input port and storing the correcting information upon an initialization of the micro-controller, wherein the correcting information is indicative of a modification for a defective information part stored in the read-only information storage memory, and a switching circuit for selectively switching the access by the address controller from the defective information part in the read-only information storage memory to the correcting information in the correcting information storage memory.