Mizunoko Shima is an isolated barren rock island and is located at the center of the Bungo channel between Shikoku and Kyushu. It is 7.5 nautical miles from the nearest shore at Kajisaki.
The light tower is a stone structure with Tokuyama cut granite stacked decoratively and 8 stories inside. The first floor is the water tank, the 2nd and 3rd floors are for storage of equipment, the 4th and 5th floors are for storage of fuel and the 6th and 7th floors are for living accommodation. The construction period of 4 years for the Mizunoko Shima Light house was the longest construction period required for any lighthouse and is considered one of the most difficult construction projects.
Since the lighthouse is on a low lying island, it was not unusual for the height of raging waves to exceed the roofs of the auxiliary buildings during the typhoon season. Records show that during the typhoon of September 22, 1912, fierce waves covered the roof of the lighthouse. Records also show that on October 1, 1941, giant waves reached the 7th floor sleeping quarters of the tower, drenched the meteorological instruments and devices such as the power generating equipment, and also destroyed the landing stage.