PURPOSE: To process history data to a timing chart output, table or graph and to improve software development by moving the record of a history to another storing means and storing the record when overflow is generated in the record at the time of software execution.

CONSTITUTION: The RAM data and I/O data of a user system 12 are executed by an emulator target CPU 2 and the data are induced through a coverage 5 to a time simulate CPU 3. Accordingly, when the sampling rate of the CPU 3 is prolonged, the history for a long time can be obtained. When a memory used for the history is filled up, the history can be continuously obtained until a host computer 1 is filled up by transferring the history data to the computer 1. Thus, the history of the software execution can be efficiently stored.