1. A character input device that comprises a display and an inputer and inputs a character according to an operation of the inputer by a user, wherein the inputer comprises at least one operation inputer that causes the character input device to execute a predetermined function according to an input from the user, the input characters belong to any one of a plurality of second character groups, each first character group comprises the plurality of second character groups, the character input device comprises: a first character group information displayer that displays first character group information about the first character group, in the display; a character selector that selects the input character from the second character group, according to the operation of the inputer by the user; and an input character determiner that determines the character selected by the character selector as the input character, according to the operation of the inputer by the user; and an input displayer that displays information about the function of the operation inputer in the display that corresponds to an arrangement of the operation inputer in the inputer, the first character group information displayer displays a part of the input characters, of the characters belonging to each of the plurality of second character groups, and a display screen of the display displays a character input window that displays information regarding a character input by the first character group information displayer, and an area that displays a game implementation situation, wherein the inputer comprises a direction inputer configured to input a direction, the character selector specifies the second character group to which the input characters belong, on the basis of the direction input to the direction inputer, and selects the characters belonging to the specified second character group, priorities are set to the characters belonging to an individual second character group, the character selector selects the input characters from the characters belonging to the second character group, according to the priorities, when the same direction as the direction which is initially input to the direction inputer to specify the second character group to which the input characters belong is input to the direction inputer, and the character selector selects the input characters from the characters belonging to the second character group, according to an inverse of the priorities, when a reverse direction, which is opposite to the direction which is initially input to the direction inputer to specify the second character group to which the input characters belong, is input to the direction inputer.