A mobile terminal device (10) includes a display unit (11), a controller (21) that displays an input field and a software keyboard on a screen of the display unit (11), a touch panel (12) that receives an input of a character string including character, symbol, or code to the input field, according to an operation of a user performed on the software keyboard, and a decider (22) that decides whether the character string inputted to the input field through the touch panel (12) satisfies a predetermined condition. The controller (21) sets the software keyboard undisplayed in the screen of the display unit (11), when the decider (22) decides that the predetermined condition is satisfied.