Music game program stored in a computer readable medium for causing a computer to output music data that corresponds to music, selected by a player, through an input device from a sound output device. The program also causes the computer to execute a procedure for displaying, on a display, a background image that corresponds to the music data. A computing a demand command invites a user to operate a specific key in correspondence with partial song data. Each demand command is produced as a command image which corresponds to each key. The command images are displayed in the order of playback of the partial song data and move on the display. A procedure for judging determines whether or not keys were operated with a predetermined timing. A procedure is also provided for outputting partial song data in which playback pitch is changes according to the result of the judgment procedure.