Jinbō Nagashiro served as a bushō during the Sengoku and Azuchi-Momoyama periods.
In 1565, following Nagamoto’s surrender to the Uesugi clan, Masuyama Castle became the main base of the Jinbō clan. The castle was located on a hill near the juncture of the Tonami, Imizu, and Nei districts in Etchū Province. Subservience to the Uesugi clan caused divisions within the Jinbō family. Notwithstanding his father’s earlier surrender, Nagazumi joined with the Ikkō-ikki forces in opposition to the Uesugi. This caused conflict with his father that resulted in Nagazumi departing and entering into service for Oda Nobunaga. As a result, Nagamoto transferred the headship of the Jinbō family to Nagashiro.
In 1571, after Nagamoto entered the priesthood and adopted the name of Sōshō, Nagashiro and his father jointly signed orders banning entry into the Monmyō Temple in Yao. This is the only known authenticated record of Nagashiro. Shortly thereafter, Nagamoto is surmised to have died.
In 1576, the base of the Jinbō at Masuyama Castle was toppled by Uesugi Kenshin. Nagashiro may have been killed in this battle as there is no record of his whereabouts thereafter.