A microcomputer includes a program memory for storing program data, a program counter for addressing the program memory, an instruction decoder for decoding the program data read out from an address of the program memory addressed by the program counter, an electrically programmable nonvolatile memory for storing address data denoting an address of the program memory where program data to be corrected is stored, and correction program data, a comparator for comparing the output from the program counter with the address data stored in the nonvolatile memory and outputting a coincidence signal when a coincidence is found therebetween, and a program correction circuit for reading out the program data from the nonvolatile memory in response to the coincidence signal, and for supplying the readout data to the instruction decoder in place of the output from the program memory.According to another feature, the microcomputer may comprise a program correction circuit wherein a correction address is supplied to a program counter, and wherein code sections are stored.