Investigators say Akitoshi Kinoshiro, 45, may have treated as many as 8,000 patients at the clinic in the Tokyo suburb of Hachioji, the Mainichi Shimbun reported. He was arrested Friday and charged with treating at least 13 patients in violation of the Medical Practioners Act.
Ken Mashimo, 45, the clinic manager, also faces charges for allegedly allowing Kinoshiro to practice medicine.
Investigators said Kinoshiro paid 10 million yen ($106,000) for the clinic in 2010 and hired several part-time doctors as staff. He allegedly began functioning as a doctor himself when he could not get coverage for Wednesdays, wearing a medical gown with the name of a reputable medical school.
Kinoshiro allegedly admitted creating a fake license by copying a real one.
In late 2012, one of the other doctors became suspicious after watching him use a bow to tie off the surgical thread used to stitch up a cut.