TOKYO (Reuters) - Japan's Supreme Court ordered a retrial for a woman who sued a former employer over a demotion during her pregnancy, handing down a partial victory that could encourage others to come forward.

The case was the first of its kind to make it to Japan's highest court, amid efforts by Prime Minister Shinzo Abe's government to boost the role of women in the economy.

The Supreme Court invalidated a ruling in favour of the former employer, made by a high court in Hiroshima in western Japan.

The Supreme Court often invalidates rulings instead of handing down its own rulings. That in turn prompts other courts to overturn earlier verdicts.

"I believe we'll see an overturned verdict," said Yumiko Akutsu, a lawyer assisting the woman, a physical therapist who is seeking compensation of 1.7 million yen, and who asked not be identified for fear of facing a backlash.

Abe has pushed for Japan's companies and government offices to hire women for top jobs, aiming for them to occupy a third of all leadership roles by 2020.

But regular workers face difficulty continuing work after pregnancy, and are often discouraged from making full use of legally-guaranteed maternity leave.

Cases of pregnant women and young mothers being harassed at work or pressured to quit have become so commonplace they have recently earned a new Japanese term: "matahara," a shortened form of "maternity harassment".

Thursday's verdict prompted the top government spokesman to underscore support for working women.

"It's against the law to terminate someone's employment, or to put someone at a disadvantage, because they're pregnant or have given birth," Chief Cabinet Secretary Yoshihide Suga told reporters.

"The government would like to cooperate with various related ministries to ensure this point is understood thoroughly, and to offer support to workers." The plaintiff was demoted after asking for a less physically demanding role while pregnant with her second child.

Her employer, a medical cooperative called Hiroshima Chuo Hoken Seikatsu Kyodo Kumiai, withdrew her management title when it moved her to a job in a hospital from a previous role that required house calls.

Two earlier trials in Hiroshima found in favour of the cooperative, which had said the removal of the woman's title was not related to the pregnancy.