PURPOSE: To ship a product cleared of deficiency accurately to consumers while enabling testing of a number of memory cards by performing a test at a high temperature.

CONSTITUTION: Table data are all written into memories of all DRAMs at a high temperature (70°C-80°C). RAS and CAS are turned to 'H' and data are checked by comparison for memory areas of all the DRAMs after a waiting for a prolonged time exceeding by 10 percent or more than a refreshing time. Then, a backup data of the data written previously is written and a waiting is set as done in the open data. Thereafter, the data is checked by comparison and when no coincidence is found, rejection is determined. If acceptance is determined, the refreshing check is ended regarding the results acceprable.