Instead, the Coast Guard is part of the Ministry of Land, Infrastructure, and Transportation (MLIT). Here's a summary pdf from MLIT's website. (Give it a minute, it seems to load very slowly on my machine.)
The JDA website in English (sorry, it's always very, very slow.)
The MLIT's website in English.
For what it is worth, the Japanese Coast Guard also sank a North Korean spy ship a few years ago.
