PURPOSE: To make character string retrieval speedy and flexible by storing document data to be retrieved while dividing them for the unit of a line and executing the retrieval by an in-line character string collation processing and an inter-line character string collation processing when retrieving character strings by parallel processors.

CONSTITUTION: A parallel character string collation part 72 is equipped with plural processor elements 721 and executes parallel processings. The character string same as a retrieving word inputted from the outside is detected out of the document data to be detected in a data base. The document data are stored in memory areas 74, which can be directly accessed by the processor elements 721, while being divided for the unit of the line. In the in-line character string collation, the data to be retrieved are read into the processor elements 721 and the character string retrieval is executed by the collation for the unit of a character in the retrieving word. When there is possibility for the retrieving word to be existent over an (m) line and an (m+1) line, a prescribed character component at the head of the (m+1) line is linked to the end of the (m) line, one line is formed and the collation is executed.