PURPOSE: To execute an exact line detecting and segmenting even when an input character string has large inclination by executing a stopgap operation in both upward and downward directions to a reciprocating scanning against the compressed bit pattern of an input character string and updating seed data at every line of one scanning.

CONSTITUTION: Compressed information (bit pattern) compressing an original image is stored in a compressed image memory 2. A CPU 5 detects a most significant bit by the compressed information of the compressed memory 2 and stores plural bit quantities into the species memory of a stopgap 3 as specified data in a column direction from the most significant bit. A stopgap circuit 9 checks a connection by species data and one line quantity of the compressed information, when the connection is found, the species data are updated. After this, only the line image data of address information are extracted by reading out from an original image memory 1 original image data of only a position corresponding to a connection result stored in a stopgap result memory 4. Thus, an exact row detecting and segmenting can be executed, even when the input character string has the large inclination.