"I am now crossing this forbidden line as a president," Roh said before stepping across the heavily-fortified frontier.
"After I return home, many more people will do likewise. Then this line of division will finally be erased and the barrier will break down.'
He said his visit would "tear down the wall of division, ease national pain from the division and lead to the path for peace and reconciliation."
Roh, who is leading a 300-strong entourage, was greeted by North Korean officials and two North Korean women wearing badges of their leaders who presented him with bouquets.
A South Korean presidential official told the AFP news agency in Seoul that Kim Jong-Il's appearance was a "good sign", as Roh had only been scheduled to meet Kim Yong-Nam, the official head of state.
"With Chairman Kim showing up in person to greet the president, the North side showed its sincerity toward the summit," the official said.
During a dinner hosted by Kim Yong-Nam, Roh told his neighbours: "It is up to us whether we can play a leading role in establishing a new order of peace in Northeast Asia."
"Let's shake off any feelings of distrust and bridge the gap of distrust we have inherited from the past as soon as possible."
During his visit the South Korean leader has pledged to foster peace and trust between the longtime foes. It is only the second such meeting ever on the divided peninsula.
He said he would build on the achievements of the first summit between Kim Dae-jung, the then South Korean president, and Kim Jong-il in 2000.
Co-operation and reunion
Al Jazeera's correspondent in Seoul
, Melissa Chan, says much has happened in the seven years since, including a steady increase in economic co-operation, and the emotional reunion of separated families from the two sides.
But North Korea
has also tested its first nuclear weapon since then – an issue that has come to dominate relations on the Korean peninsula.
Before his departure from Seoul, Roh said he would "hasten the slow march" of reconciliation between the two countries which remain technically at war since the 1950-53 Korean War ended in an armistice.
"I intend to concentrate on making substantive and concrete progress that will bring about a peace settlement together with economic development," he said ahead of the 200-km road journey to the North Korean capital.
For the first summit in 2000, Kim Dae-jung travelled to Pyongyang by air.
Reports have said Roh may promise billions of dollars in aid to North Korea's economy during his visit.
But critics have expressed concern that Roh may pledge so much in aid that North Korea will feel it can reject incentives offered by regional powers to stop its nuclear arms programme.
Others say that with just a few months left on his presidency, Roh may make unrealistic promises because he will not have to deliver on them.
South Korean activists and defectors from the North Korea have staged small protests against the summit, branding Roh a pro-Pyongyang leftist.
The Chosun Ilbo newspaper warned in an editorial that Kim "may use his old tactic to wrest only economic support from South Korea while putting aside important issues for talks with the United States."
South Korean officials have said they do not want to sour the mood by pushing Pyongyang on what they call "sensitive issues" during the summit.
So Pyongyang's nuclear weapons programme and human rights issues are to be side-stepped when Roh meets Kim for the three days of talks.