The election board of Takatsuki, Osaka Prefecture, issued 62 voters with ballot papers for the constituency and proportional-representation segments of the House of Councillors election in the wrong order, it said Sunday.
As a result, their votes may be invalidated, it said.
The mistake occurred at two polling stations in the city.
Election board officials should have issued ballot papers for the constituency segment first, followed by ballot papers for the proportional-representation segment. But they issued the papers in reverse order, so that if the 62 voters inadvertently wrote their choice of candidate on the wrong paper, their votes will not count.
A similar mistake occurred at a polling station in Isa, Kagoshima Prefecture, where 18 voters were affected. The local election board apologized to them as their votes may not count.
In Shimanto, Kochi Prefecture, meanwhile, the local election board issued ballot papers to a woman in her 80s, although she had cast an early vote, it said.
She accompanied a friend to a polling station Sunday and was allowed to vote as an election board official neglected to check if she had already cast a vote.
She later informed the officials that she had cast an early vote, but both her votes will stand because there is no way to identify her ballot papers.