1. A game system comprising: a plurality of gaming machines each belonging to one of a plurality of groups; and an external device configured to be in communication with each of the plurality of gaming machines, wherein each of the plurality of gaming machines include a reader configured to read identification information identifying a player and a game controller configured to: transmit the identification information read by the reader to the external device; receive game rate data from the external device based on the identification information, wherein the game rate data is a fee for playing a single game or a fee to be bet on a single line; automatically set a game rate from a plurality of available game rate settings without receiving a user input to set the game rate based on the received game rate data; and execute a process according to a game based on the set game rate, wherein the process results in a payout in coins, a number of which is calculated by multiplying the set game rate by a number corresponding to a winning symbol combination, and wherein the external device includes a controller configured to execute a game rate determining program, and by executing the game rate determining program: receive the identification information from each of the plurality of gaming machines; select one of a plurality of levels based on the identification information received from each of the plurality of gaming machines; determine a ratio of a number of the plurality of gaming machines of the plurality of levels corresponding to each of the plurality of groups; select a game rate for each of the groups based on the ratio; and transmit, to each of the plurality of gaming machines, the selected game rate data including the selected game rate corresponding to a respective one of the plurality of groups to which each gaming machine belongs.