Kameda, 21, grabbed the belt with 116-110, 114-112, 116-110 after the full 12 rounds.
He had no knock-down but kept calm despite repeated clinch work by Kaowichit, who suffered one-point deductions in the sixth and 11th rounds for repeatedly holding Kameda.
The Japanese fighter now stands with 16 wins with 11 knock-outs and two losses, including a loss by judges' scorecards to the veteran Thai fighter in October.
For Kaowichit, 33, it was his second loss, with 48 wins including 20 knock-outs and one draw.
"I have been told that I have no boxing sense, no talent. But I was able to continue because of my family," tearful Kameda told roaring fans after the victory.
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