"I hope my election victory will help our fellows nationwide to have hope for tomorrow, as many of them cannot accept themselves, feel lonely and isolated and even commit suicide," he told AFP.
Ishikawa, 36, won a seat in a Tokyo ward assembly in local elections on Sunday. Prior to his victory, no openly homosexual politician had won office in Japan.
He said he hoped his victory would help lesbian, gay, bisexual and transgender people.
"Many LGBTs, or sexual minorities, realise the fact when they are at elementary and junior high schools, many of which are operated by the municipality," Ishikawa said.
"As a ward assembly member, I would like to reinforce support to LGBT children at schools."
Ishikawa disclosed that he is gay in his autobiographical "Boku No Kareshi Wa Doko Ni Iru" (Where Is My Boyfriend?)," published in 2002.
"Many readers of my book told me that they are isolated and the situation I wrote about in the book is so similar to theirs. So I started to host events that offer opportunities to have links with friends," Ishikawa said.
He founded the non-profit organisation "Peer Friends", which hosts events in Japanese cities to provide young gay men with opportunities to meet other gays.
Since February 2010, he has served as a private secretary to Mizuho Fukushima, the leader of the Social Democratic Party, a small opposition group.