1. A playback apparatus for playing back a graphics stream and a video stream, wherein the graphics stream includes one or more interactive control segments and one or more graphics data pieces, each interactive control segment includes page information and time-out information, each page information includes one or more button information pieces, each button information piece realizes an interactive screen structure by displaying each graphics data piece as a state of a corresponding graphics button material, the time-out information indicates a time on a playback time axis of the video stream at which the interactive screen structure is ended, the playback apparatus comprises: a plane memory storing therein graphics to be played back; a decoding unit (i) obtaining a page including a plurality of graphics button materials by decoding the graphics stream, and (ii) writing the obtained page to the plane memory; a page number register storing therein a page number of a current page; and a button number register storing therein a button number of a current button, which is one of the button materials in a selected state on the current page, when a selection of one of the button materials on the current page is confirmed, the decoding unit executes a set command that sets a new button number in the button number register, the button number stored in the button number register becomes invalid when a current playback time has reached the time indicated by the time-out information, and the invalidation of the button number is performed by the decoding unit deleting the written page from the plane memory.