A counting device (100) provided with a subtree generating part (123) for generating first subtree comprising a first sentence and a second subtree comprising a second sentence. The counting device (100) is provided with: a categorizing part (125) for categorizing the first subtree in the same group as the second subtree when it is determined that a first expression represented by the first subtree and a second expression represented by a second subtree represent a matching content; and an output part (127) for outputting the number of subtrees categorized in the group, or an expression represented by a plurality of syntax trees or one of the subtrees categorized in the aforementioned group.