Abstract: Melody Slot Machine HD is an application that allows one to generate melodies using music structures while playing a slot machine. The user can create new melody combinations by rearranging melody variations using the slot machine. When the user composes a melody with variations, the structure of the melody is analyzed using a theory of music known as the generative theory of tonal music. Even if the melody switches variations in the middle, the overall structure will not be disrupted. Our original Melody Slot Machine has been exhibited in academic conference as a demo system. Due to Covid-19, however, it has become difficult to exhibit in places where many people gather, so we developed an app version for the iPad, Melody Slot Machine HD, to give many people access to it through the Appstore. We conducted an experiment to evaluate Melody Slot Machine HD, and the results indicate that when five participants listened to new variations of melodies generated by random combinations using Melody Slot Machine HD, 85.6% of the melodies were judged as natural or almost natural.