PURPOSE: To effectively mechanize and automate such tasks as the development, the test, and the maintenance of software by searching the patterns with use of a mask pattern.

CONSTITUTION: A mask pattern used for designation of C (character) and X (hexadecimal) is decided together with the start and end addresses in a mask pattern command analyzing process 21 where the contents pointed by the operands of mask pattern commands 11 and 12 given from a user are interpreted. A fault memory information read processing means 22 evolves the contents covering a start address through an end address to a memory from a fault memory information store medium 30. Thus the fault memory evolving information 25 is obtained. Then a mask pattern search processing means 23 compares the mask pattern designated by the user with the contents evolved to the memory and retrieves a coincident area. Thus the development, the test, and the maintenance of software are effectively mechanized and automated.