An AND operation is performed for an integrated appearance map of a compression code of character data “”, an integrated appearance map of a compression code of character data “”, and an integrated deletion map for a segment. The AND result is “1100” and it is found that the character data “” and “” are likely to be present in the segments (sg1(1)) and (sg1(2)). Since the segments are specified from the AND result, the AND operations are performed. As a result, the segments are specified and the AND operations are performed. As a result, a file number 3 is specified from the segment (sg0(1)) and a file number 19 is specified from the segment (sg0(5)). Therefore, it is found that both of the character data “” and “” are present in compression files (f3) and (f19).