- Titles: Dewa no kami
- Distinction: Tokugawa retainer
- Son: Ôsuga Tadatsugu [大須賀忠次]
- Japanese: 大須賀忠政 (Oosuga Tadamasa)
Tadamasa was the eldest son of Sakikabara Yasumasa. His grandfather on his mother's side, Ôsuga Yasutaka [大須賀康高], had no sons of his own and so Tadamasa was adopted by him to carry on the Ôsuga name. Yasutaka died in 1589 and Tadamasa succeeded him, also being given the use of the name 'Matsudaira' [松平] by Tokugawa Ieyasu. When the Tokugawa house was relocated to the Kanto following 1590, the young Tadamasa was established in Kazusa Province with a 30,000-koku fief. In 1601 his fief was moved to Tôtômi Province and increased to 60,000 koku. He fell ill in 1607 and died in Kyoto in the 9th month.