Included is an instruction unit configured to instruct input of a character as a part of a character string; and a control unit configured to, under a restriction that any of a specific character group is allowed to be input in neither of a plurality of predetermined positions of the character string, upon any of the specific character group being instructed by the instruction unit to be input in at least one specific position of the plurality of predetermined positions, prohibit input by the instruction and, upon any of the specific character group being instructed by the instruction unit to be input in a position different from the specific position, enable input by the instruction.