Kumagai, who joins Roma from Germany's Bayern Munich, has penned a two-year deal with the Italian side.
"I'm thrilled to join Roma and can't wait to play for this club," the 32-year-old midfielder-defender said.
"I'm grateful to Roma for showing their faith in me, and I'll give my all to repay the confidence shown in me and meet the team's expectations. I want to make history for this club."
👋 Welcome to Roma, Saki Kumagai! 🇯🇵
— AS Roma Women 🇮🇹 (@ASRomaWomen) June 5, 2023
The highly-rated Japanese midfielder joins the Giallorosse! 🐺#ASRomaWomen #ASRoma pic.twitter.com/ZLSPqAf0gT