Abstract: A debugging system is adapted to perform debugging by employing a virtual address in a computer system which includes a microprocessor incorporating a virtual storage function and a function for outputting a normal bus cycle corresponding to a real address in a normal operation and a function for outputting a debugging bus cycle corresponding to a virtual address. The microprocessor outputs a signal indicative of a kind of access and a signal indicative of an outputting state of a virtual address during outputting of the virtual address in the debugging bus cycle. A memory device is connected to the microprocessor through an address bus and a data bus. The debugging system includes a bus monitoring means for monitoring output of the processor, the output from bus cycles and transfer data. The bus monitoring means includes a debugging means for performing the debugging process associated with the virtual address.