Pae Jun Ho was arrested after entering the country as a tourist Nov. 3, CNN reported.
The Korean Central News Agency said Pae had confessed and would soon be taken to the Supreme Court "to face judgment."
The news agency's report said, "In the process of investigation he admitted that he committed crimes aimed to topple the DPRK with hostility toward it," Yonhap New Agency reported.
South Korean media identified the man as Kenneth Bae and said he had entered North Korea with five other tourists.
Since 2009, North Korea has detained four American citizens but released them following negotiations.