Prime Minister Shinzo Abe on Monday congratulated independence-leaning Tsai Ing-wen for her election as president of Taiwan.

"I would like to express congratulations from the bottom of my heart. I'm hoping that the cooperative relationship between Japan and Taiwan will advance further," Abe told a session of the Upper House Budget Committee.

"Taiwan is an old friend of Japan's," Abe said. "Deciding on a leader through an election based on freedom of speech, the presidential election is a testimony to freedom and democracy in Taiwan."

Tsai, leader of the main opposition Democratic Progressive Party, won Saturday's election with 56 percent of the vote against 31 percent for Eric Chu of the China-friendly Nationalist Party, which has held the presidency for the last eight years.

She will formally take the oath of office May 20, when she will become Taiwan's first female president.

Chief Cabinet Secretary Yoshihide Suga said Monday that Japan "welcomes" Taiwan's interest in joining the Trans-Pacific Partnership and "would like to have fruitful discussions" on the matter.

"If (Taiwan) were to join the TPP, it would significantly contribute to the stability and prosperity of the (Asia-Pacific) region," Suga said at a news conference.

Along with Taiwan, other Asian economies such as Indonesia, South Korea, the Philippines and Thailand have shown interest in joining the 12-member TPP, which, once put into force, would represent around 40 percent of the world economy. China is not a member.