Local police on Jindo island said the body of vice principal Kang Min-Kyu, 52, was found near the gymnasium where relatives of the 268 people still missing from the ferry disaster have been staying.
"The precise cause of death is still under investigation," one police official told AFP.
Yonhap news agency cited police as saying he was found hanging from a tree having apparently committed suicide.
They were taking the ferry for a school excursion to the popular southern resort island of Jeju.
The vice principal was among 179 people who managed to escape the ferry in the few hours before it capsized and sank.