CHIBA - A manager at a Japan car company was found to have worked himself to death after clocking overtime for his staff, said the local authorities.

The family of the 48-year-old man has filed a lawsuit in the local district court against Honda Cars Chiba, an affiliate of Honda Motor, according to The Asahi Shimbun.

His family is seeking unpaid salary for the overtime he worked as well as compensation for the man's suffering.

The Asahi Shimbun reported that the man, who was not named, committed suicide in December last year (2016), quoting a family representative who made the revelation on Tuesday (Dec 19).

The Chiba Labour Standards Inspection Office officially recognised his death as karoshi, or death from overwork.

The man became the manager at a sales outlet of Honda Cars Chiba in March 2015. He had worked more than 80 hours of overtime a month, which happened twice, according to The Asahi Shimbun. Once, he worked 17 consecutive days, and at another time, 13 days in a row.

The man had put in extra hours so that his staff did not have to work overtime.

He went missing in June 2015 and when he returned to work two months later, he was diagnosed with stress-induced depression caused by several work-related issues including overwork as well as sales deficits at the outlet, The Asahi Shimbun reported.

The company fired him in August 2015 for being absent for two months without permission. He killed himself in December last year.

After his death, the man's wife said that some mid-level executives have no choice but to shoulder the burden of more work.

"I would like (the company) to take (what my husband faced) seriously, and take actions over it," she said, as quoted by The Asahi Shimbun.

A lawyer representing Honda Cars Chiba declined to comment as the case is now before the court.

Professor Emeritus Koji Morioka at Kansai University, who specialises in the theory of corporate community, said that while the Japanese society is increasingly against excessive overtime at work, the burden faced by mid-level executives has shown no signs of abating. This is because of a lack of manpower and growing workload.

"Companies need to keep tabs on the working hours of managers," Prof Morioka told The Asahi Shimbun.