An Interactive Graphics Decoder 13 decodes a graphics stream, and overlays a Page including a plurality of Buttons on a moving picture. The Interactive Graphics Decoder 13 then executes a command corresponding to one of the plurality of Buttons on the Page, to thereby perform (1) a control of switching the Page to another Page and (2) a control of specifying a Button to be set in a selected state on the other Page. A judgment is made as to whether a button number of the specified Button is invalid. If the button number is invalid, an alternative value is written in a status register.