When a function is selected, and then, a character string to which the function is executed, an operation of selecting the character string is facilitated in order to reduce an operation burden of a user.The present invention is characterized by including a display unit that displays content information including a character string; a memory unit that stores a character type-function correspondence information in which functions and a character type of a character that is a subject to which the corresponding function is executed are associated with each other; a function selection unit that selects a function to be executed; a character selection unit that selects a desired character string in the content information displayed on the display unit, after the function is selected; a character identification unit that refers to the character type-function correspondence information in order to determine whether a character having a valid character type to which the selected function can be executed is present or not in the character string selected by the character selection unit; and a valid character string decision unit that decides a valid character string, which is a subject to which the function is executed, from the selected character string, when the character identification unit determines that the character having the valid character type is present.