Miwa Sado, a political journalist for the country's national broadcaster, suffered a heart failure in July 2013, but her employer only made the tragic case public this week.
Sado, who was 31 at the time, was a reporter in charge of covering the Tokyo Metropolitan Government.
The broadcaster NHK said it kept track of her working hours but accepted there were areas that needed to be improved, according to the Japan Times.
Masahiko Yamauchi, an official at NHK's news department, said the incident was a 'problem for our organization as a whole, including the labor system and how elections are covered.'
