on the outside i can read 花文透鐔 Kamon Sukashi tsuba and on top right 無銘 mumei
Inside seems to be 丸形 Maru gata and the rest is quite hard for me, there's another 無銘 mumei and the signature is the one of Kanzan
i'm not an expert of mirrors, but sure they value more than some euro
WIth a quick research i found this sold on catawiki that has exactly same design as yours https://www.catawiki.it/l/19624787-bronze-hand-mirror-signed-fujiwara-masashige-Japan-early-20th-century-meiji-period
the price looks quite cheap especially considered the lacquered box.
Mirrors from that maker are also exhibited in museums https://www.britishmuseum.org/collection/object/A_1944-0401-2
If original it would be Early 20th century, around Meiji Period.
The flat side would be litterally mirror polished, usually those mirrors also have an handle attached, but maybe this one being small didn't need it or got broken?