8. The form recognition apparatus according to claim 7 , further comprising: a storage unit capable of storing a database in which headline wordings that may appear in a unit table structure being a unit for entering one or more pieces of related data in the form are defined in a hierarchical structure for each unit table structure, wherein the table structure determination unit determines the entire table structure existing in the form image, referring to a database stored in the storage unit.
8. The form recognition apparatus according to claim 7 , further comprising: a storage unit capable of storing a database in which headline wordings that may appear in a unit table structure being a unit for entering one or more pieces of related data in the form are defined in a hierarchical structure for each unit table structure, wherein the table structure determination unit determines the entire table structure existing in the form image, referring to a database stored in the storage unit. 9. The form recognition apparatus according to claim 8 , wherein the hierarchical structure includes a first layer in which one or more headline wordings are defined, a second layer in which a first representative headline being a headline wording that represents a headline wording defined in the first layer and can be replaced with another headline wording and a third layer in which a second representative headline being a headline wording ordered higher than the first representative headline in the table structure, and the table structure determination unit sets a range of the unit table structure having the second representative headline, on the basis of an extraction result of the second representative headline, by the character string extraction unit, evaluates other headline wordings extracted in the set range and specifies a headline wording existing in the unit table structure.