As in 1219, MINAMOTO no Sanetomo, the third Shogun was assassinated and Yoritsune KUJO left the capital to go to Kamakura as successor Shogun, Tokinaga went down to Kamakura with his son, Nagase, and served as Gon-ji of Shogun family.
承久元年（1219年）に第3代将軍・源実朝が暗殺され、九条頼経が後継の将軍として鎌倉に下向すると、子の長世と共に鎌倉に下向して将軍家の権侍医として仕えたという。