In 1604, at the age of 26, his father Masatsugu died suddenly, whereupon Masakazu succeeded to the family estate, taking care of Matsuyama Castle (Bicchu Province); subsequently, in 1617 he became a daimyo (feudal lord) upon receiving a Shuinjo(shogunate license to trade), and two years later he was transferred to the Omi Komuro Domain.
慶長9年（1604年）26歳のときに父正次が急死し、家督を継いで松山城(備中国)を預かり、その後元和2年（1617年）に朱印状を得て大名となり2年後近江小室藩に移封される。