It's Biruma no Tategoto (CLICK HERE, HERE, and HERE). There's a remake (1983), too.
The song was translated and introduced to Japan in 1885(?) as a schoolsong: "Hanyu no Yado". Amelita Galli-Curuci's recording was inserted in anime movie Hotaru no Haka (Grave of the Fireflies, 1988).

~Masato