TOKYO (AFP) - The first female head of Japan's largest trade union vowed on Friday (Oct 22) to fight workplace sexism in a country where women still face pressure to "become a good wife and a good mother".

Ms Tomoko Yoshino, 55, said she felt a "great responsibility" to improve opportunities for women in Japan, which is ranked 120 out of 156 nations in the World Economic Forum's latest global gender gap report.

She became president this month of the Japanese Trade Union Confederation, known as Rengo, which has about seven million members.

"I felt that it was up to me to break through this Japanese glass ceiling and not pass up on this opportunity," Ms Yoshino told reporters at the Foreign Correspondents' Club of Japan.

She pledged to work towards a society "in which it is comfortable, or easier, for women to work and to live".

Many women in Japan leave the workplace when they have children, and find themselves disadvantaged if they try to return, she said.

This has led to the "very low" representation of women in leadership roles, including in politics, with female candidates accounting for just 18 per cent of those running in Japan's general election on Oct 31, Ms Yoshino said.

Just three out of 21 ministers in Japan's Cabinet are women.

"The division of gender or sex roles in Japan is still very deeply rooted, whether within the workplace, the community or the family," Ms Yoshino said.

"This is something which is still exceedingly strong... the expectations on women that what they should be aiming for is to become a good wife and a good mother."

Ms Yoshino, who is the first woman to lead Rengo since it was founded in 1989, slammed Japan's gender-gap index ranking - where it slots in between Angola and Sierra Leone - as "an extremely low position for a so-called advanced or developed country".