A mobile terminal device, comprising: a display configured to display a first display section including a first plurality of operation keys including operation keys corresponding to character inputs and to display a second display section including a second plurality of operation keys configured to move in a horizontal manner; a touch sensor configured to receive a touch input corresponding to at least one of the first plurality of operation keys displayed in the first display section and the second plurality of operation keys displayed in the second display section; and a controller configured to select the second plurality of operation keys displayed in the second display section based on a predetermined set of operation keys stored in memory, and to switch the second plurality of operation keys displayed in the second display section to a third plurality of operation keys based on a moving touch input received at the second display section, wherein the touch sensor is configured to detect the moving touch operation at one of the second plurality of operation keys in the second display section, the second plurality of operation keys are assigned to a first page of operation keys and the third plurality of operation keys are assigned to a second page of operation keys, the controller is configured to control the display to switch from displaying the first page to the second page based on the moving touch operation, and the circuitry is configured to control the display to display a page indicator in the second display section graphically indicating a position of a currently displayed page among a plurality of available pages of operation key display groups; wherein the controller is configured to obtain a usage frequency of each of the second plurality of operation keys, and change positions of the second plurality of operation keys based on the usage frequency, wherein a key of the second plurality of operation keys having a usage frequency above a predetermined threshold is displayed on the first and second page of operation keys. a display configured to display a first display section including a first plurality of operation keys including operation keys corresponding to character inputs and to display a second display section including a second plurality of operation keys configured to move in a horizontal manner; a touch sensor configured to receive a touch input corresponding to at least one of the first plurality of operation keys displayed in the first display section and the second plurality of operation keys displayed in the second display section; and a controller configured to select the second plurality of operation keys displayed in the second display section based on a predetermined set of operation keys stored in memory, and to switch the second plurality of operation keys displayed in the second display section to a third plurality of operation keys based on a moving touch input received at the second display section, wherein the touch sensor is configured to detect the moving touch operation at one of the second plurality of operation keys in the second display section, the second plurality of operation keys are assigned to a first page of operation keys and the third plurality of operation keys are assigned to a second page of operation keys, the controller is configured to control the display to switch from displaying the first page to the second page based on the moving touch operation, and the circuitry is configured to control the display to display a page indicator in the second display section graphically indicating a position of a currently displayed page among a plurality of available pages of operation key display groups; wherein the controller is configured to obtain a usage frequency of each of the second plurality of operation keys, and change positions of the second plurality of operation keys based on the usage frequency, wherein a key of the second plurality of operation keys having a usage frequency above a predetermined threshold is displayed on the first and second page of operation keys.