- Birth:1581
- Death:1607
- Titles: Dewa no kami
- Distinction: Tokugawa retainer
- Son: Oosuga Tadatsugu [大須賀忠次]
- Japanese: 大須賀忠政
Tadamasa was the eldest son of Sakikabara Yasumasa. His grandfather on his mother's side, Oosuga Yasutaka [大須賀康高], had no sons of his own and so Tadamasa was adopted by him to carry on the Oosuga name. Yasutaka died in 1589 and Yasumasa 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 Yasutaka was established in Kazusa Province with a 30,000-koku fief. In 1601 his fief was moved to Tôtômi and increased to 60,000 koku. He fell ill in 1607 and died in Kyoto in the 9th month.