The Diet on Wednesday passed a bill seeking to boost the number of female lawmakers and assembly members in a nation where women have long been underrepresented in politics.

The measure, approved unanimously by the Upper House, urges each political party to make every effort to try and "equalize as much as possible" the number of male and female candidates it fields for national and local elections.

Although it heralds a significant step toward increasing the presence of females in the male-dominated world of Japanese politics, the bill has no legally binding power, only stipulating political parties need to "make voluntary efforts" to even the playing field in terms of gender. A failure to achieve the goal entails no penalty.