A receiving unit receives information selected by a user on an operating screen. A detecting unit detects a function executing part corresponding to the information received by the receiving unit. A determining unit determines that the user authentication is required when a function is to be executed, when “the user authentication is required” is set for at least any one of a function allocated to a function executing part that is detected by the detecting unit, the function allocated to another function executing part, and the operating screen that includes the function executing part to which the function is allocated. A function executing unit executes a function allocated to the function executing part selected by the user, wherein the user is authorized to execute the function.