At Bristol Crown Court, the 53-year-old confessed to making indecent photographs of children, along with possessing more than 400 images.
He pleaded guilty to 12 counts of indecent assault against five young women, but not guilty to a charge of rape, which was changed to indecent assault.
Former BBC Radio Bristol and BBC Somerset presenter Rowell was charged last April with a range of offenses dating back to the late 1980s and early 1990s.
He spoke today only to confirm his name and enter his pleas. He has been remanded in custody until sentencing on March 2.
Prosecuting lawyer Ian Fenny told Judge David Ticehurst: "Your Honour is right to say that this defendant accepts all the serious allegations against him."
Fenny said that the prosecution accepted the four not guilty pleas, including the rape charge that was changed to indecent assault.
Edward Burgess, the lawyer representing Rowell, told the court that his client was aware a custodial sentence was expected to follow.
Judge Ticehurst said it was "only right" that Rowell's victims, who cannot be named due to legal reasons, should be in court to see him sentenced in March.
Rowell hit the headlines in March 2011 after failing to turn up to work at BBC Radio Bristol and BBC Somerset. Fears were raised after his car was found left in a supermarket car park.
However, the father-of-one was later found in Cumbria, after which he was arrested by police, who had already raided his home and found the indecent images on his computer
Rowell had read the news bulletin on ITV West for ten years, but most recently presented the Afternoon Show on BBC Radio Bristol and BBC Somerset.
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