The 23-year-old Kameda built up a solid lead through the first nine rounds at Saitama Super Arena and held on to win despite a desperate attempt by Naito to erase the deficit.
The judges scored the bout 116-112, 117-111, 117-111 in favor of Kameda.
"I want to thank all the fans who supported me," Kameda said. "This is like a dream."
The 35-year-old Naito was making the sixth defense of the title he won by defeating Thailand's Pongsaklek Wonjongkam in 2007.
The undefeated Kameda, who has been criticized in Japan for his brash behavior in and outside the ring, was making his first attempt at a major world title. He improved to 22-0 (14 KOs).
Naito, who defeated Kameda's brother Daiki by unanimous decision for the first defense of the title in October 2007, dropped to 35-3-3 with 22 KOs.
Naito said before the bout that he would consider retirement if he lost.
