Provided are an apparatus and method for inputting a graphical password that use representative pictures and elemental pictures of a graphic to form a graphical password and that receive the graphic via a wheel interface and a select button for user authentication. The apparatus includes: an input unit having a wheel interface and a select button; a display for displaying a graphic consisting of representative pictures and elemental pictures, and displaying a changed graphic in response to an input from the wheel interface; a memory for storing a graphical password of a user; and a controller for recognizing, when the select button is pressed, the graphic displayed on the display as a user-input graphical password, and determining whether the input graphical password matches the stored graphical password for user authentication. Thus, it is possible to increase the number of cases for a password using a wheel interface for a higher security level of an embedded system that has a low security level due to a limited type and length of letters input as a password.