5. The generation apparatus according to claim 4 , wherein the processor is configured to: generate a tree structure in which the plurality of words is represented based on the grammatical or conceptual relation, and generate the contracted sentence by sequentially connecting the words of which first index is equal to or larger than another threshold or the words having the indispensable connection from a starting point word of the tree structure.
5. The generation apparatus according to claim 4 , wherein the processor is configured to: generate a tree structure in which the plurality of words is represented based on the grammatical or conceptual relation, and generate the contracted sentence by sequentially connecting the words of which first index is equal to or larger than another threshold or the words having the indispensable connection from a starting point word of the tree structure. 9. The generation apparatus according to claim 5 , wherein the processor is configured to: set the threshold in states, generate a plurality of contracted sentences including the contracted sentence according to the threshold set in states, and select the contracted sentence from among the plurality of contracted sentences based on a length which is designated.