A game apparatus includes a CPU core, and the CPU core executes a music playing game according to a game program. During the game, a player plays a guitar as if he or she plucks the strings displayed on an operation screen while viewing a musical score of a desired music (tune) by utilizing a stick. During playing, the timing of the tempo of the music being played by the player is detected, and when the timing of the head of the quarter note in the detected tempo and the timing at which the player currently plays are coincident, a sound effect such as clapping sound, and the like is output. The volume of the clapping sound is increased when the tempo is stable, and decreased when the tempo is unstable.