1. A system for supporting communication among users, comprising: a storage device for storing each of at least one communication means used by each user, in association with a score indicating a skill level of the user for transmitting and receiving information when using the communication means and a conversion accuracy of each conversion means that converts one communication means into another communication means; a search unit for searching out, from the storage device, at least one first communication means used by a first user and at least one second communication means used by a second user, wherein each communication means can be used in common by both the first and second user; and a selection unit for reading, from the storage device, the scores of the first and second users for each of the searched-out communication means, and then selecting a communication means to be used in the communication between the first and second users, on the basis of the read scores; wherein the search unit searches out, from the first communication means, any of the first communication means that can be matched with any of the second communication means through conversion using any of the conversion means and searches out a plurality of conversion paths each allowing at least one of the conversion means to convert the first communication means into any one of the second communication means; and the selection unit reads, from the storage device, the score corresponding to the searched-out first communication means, the conversion accuracy corresponding to the conversion means that causes the first communication means to match the second communication means, and the score corresponding to the second communication means; the selection unit determines a communication establishment possibility between the first and second users, wherein each of the scores and the conversion accuracy takes a value between zero and a predetermined constant value, by calculating, for each of the searched-out conversion paths, a product of the score corresponding to the first communication means before conversion, the conversion accuracy corresponding to each of the conversion means on the conversion paths, and the score corresponding to the second communication means after conversion, and determining the communication establishment possibility between the first and second users on each of the searched-out conversion paths on the basis of the calculated product; and the selection unit selects a communication means to be used in the communication between the first and second users based on the communication establishment possibility.