This appears to be sheet music for the mandolin duet "Utile Dulci," which was likely sold at the musical instrument store "The Kyoyeki Shosha" (now Yamaha) in Ginza, Tokyo. Nowadays, the mandolin is played in mandolin orchestras and ensembles, as well as solo, or with guitar or piano. There are also commercially available collections and scores, but the number of pieces for mandolin duet seems to be surprisingly small. Based on the pencil markings, this is an antique sheet music collection from 1927 (almost 100 years ago). However, the sheet music itself seems to be an import from Florence, suggesting it could be even older. There is a notation indicating a transcription from 1499. This is a very rare and valuable item. The inside is also relatively clean, so the music can actually be read. Collectors, don't miss out!