Abstract: A microcomputer includes: a memory; a CPU which decodes memory data stored in the memory to execute an instruction; a debug control section for instructing the microcomputer to perform a debug operation according to an instruction from an external debug instruction device which is connected to the microcomputer; and an authentication section for performing, when the external debug instruction device is connected to the microcomputer that is in a normal operation, an authentication as to whether to allow the debug operation to be performed, wherein the memory data of the memory is prevented from being read out to outside of the microcomputer during a period between connection of the external debug instruction device to the microcomputer and success of the authentication by the authentication section.