The robot, which has not yet been identified, is said to have been fired eastwards towards the sea.
The Japanese Coast Guard reports that what may be a North Korean robot has landed in the sea 17 land miles from the Japanese coast.
A source in the Japanese military tells AFP that it is in Japan's exclusive economic zone.
The robot is then estimated to have flown for about an hour.
This is the twelfth time so far this year that North Korea has conducted high-profile weapons tests.
The last time was on Sunday.
On two occasions in recent weeks, North Korea is judged to have conducted tests involving components from Hwasong-17, the country's largest intercontinental robot to date.
South Korea and the United States suspect that it will be fully tested in the near future.