Kamimura, a former member of a Japanese boy group named ONE N' ONLY, was arrested in the southern Chinese city in March.
In the same month, his contract was terminated due to a serious compliance violation. In April, he pleaded not guilty.
He allegedly touched the interpreter's thigh repeatedly during a celebratory dinner at a restaurant.
During the trial in July, the interpreter testified through a live video link that Kamimura had invited her to a bathroom elsewhere.
After she dismissed the request and told him she had a boyfriend, Kamimura continued to touch her thigh, she said.
The defence argued the interpreter exaggerated her claims and the alleged bathroom invitation might not have been based on improper motives.
Judge Peter Yu handed down the conviction on Wednesday, saying Kamimura touched the interpreter in a caressing nature that implicitly carried a sexual undertone and had indecent intent.
After the verdict was announced, a few of Kamimura's fans wept in the courtroom.
But Kamimura looked relieved when the judge issued a fine of $HK15,000 ($A2900) and no prison term.
The maximum penalty for the charge is 10 years of imprisonment.
The singer's supporters, including some from Japan and mainland China, formed long lines inside the court building to secure a seat in the main courtroom before the hearing.
Others from mainland China who attended said they were not fans but wanted to learn more about the case.
Kamimura also is an actor who appeared in several TV dramas including the boys' love series Our Youth and the popular drama Ossan's Love Returns.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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