Abstract: A scale indicator has a key selecting device and multiple illuminating devices. The key selecting device is arranged on the keybed of the keyboard. The player can use the key selecting device to choose the musical key for the music that he or she wants to play. Each illuminating device is electrically connected to the key selecting device and corresponds to one of the keys of the keyboard instrument. The illuminating devices will show a note for the corresponding key after the player sets the key selecting device to a desired musical key. This can show the player the notes to which the keys of the keyboard respectively corresponded. To learn the keyboard instrument becomes easier.