1. An information spread scale prediction device which acquires text data from a specific website via the Internet, predicts number of future contributions made to the website based on the text data, and outputs a prediction result thereof, the information spread scale prediction device comprising: a learning text data input unit which acquires the text data from the specific website as learning text data; a node influence learning unit which classifies the learning text data by each topic, calculates influence for the number of contributions by each group to which a node indicating a specific user belongs for the topic from the number of contributions of each of the classified topics, and stores a result thereof as learning data to a storage module provided in advance; a prediction text data input unit which acquires the text data from the specific website as prediction data after storing the learning data; and a future contribution number prediction unit which classifies the prediction text data by each topic, predicts the number of contributions of the topics at a specific future time based on the number of contributions by each of the classified topics and the learning data, and outputs a result thereof to an output module provided in advance.