1. A generation apparatus that generates a contracted sentence in which one part of a plurality of words included in a sentence is removed, the generation apparatus comprising: a memory configured to store a first index for determining whether two words are left as a pair in the contracted sentence, for each characteristic between the two words being connected to each other in the sentence through a grammatical or conceptual relation; and a processor coupled to the memory and configured to: generate the contracted sentence by removing the one part of the plurality of words based on the first index corresponding to every pair of two words connected to each other with the grammatical or conceptual relation, and output the contracted sentence.