Japan's government said the trade ban would send a strong message
Japan has banned all exports to North Korea after the North conducted nuclear and missile tests last month.
The move is expected to have little impact, as Japan banned imports after the North's first nuclear test in 2006.
Meanwhile, China has pledged to implement tougher sanctions against the North approved by the UN last week.
Also, a Chinese official said he did not know of a reported visit to Beijing by a son of Kim Jong-il, said to be the chosen heir to the North Korean leader.
In Tokyo, the Japanese cabinet approved the trade ban amid fears that Pyongyang is preparing to conduct a third nuclear test.
The UN Security Council voted on Friday for tougher sanctions after a second nuclear test was conducted on 25 May.
A Japanese government official said the export ban was more than a symbolic gesture.
Tens of thousands rallied in Pyongyang against UN sanctions
"What's most important is that North Korea make the right response... to Japan's strong message, even though there are people who point out the volume of exports is small," said Chief Cabinet Secretary Takeo Kawamura.
Japan is so concerned because much of its territory could be hit by North Korean mid-range missiles, says the BBC's Roland Buerk in Tokyo.
The tougher UN sanctions include the inspection of ships suspected of taking banned cargo to and from North Korea, a wider ban on arms sales and further measures to cut Pyongyang's access to international financial services.
Following the resolution, the North said it would start enriching uranium and use all its plutonium for nuclear weapons.
North Korea's largest trading partner, China, said it would take action to implement the new sanctions, but urged caution.
"Like other members of the Security Council, China will implement the resolution earnestly," said Chinese foreign ministry spokesman Qin Gang.
"We hope the relevant parties can remain calm and exercised restraint, solve relevant issues through dialogue and consultations and refrain from taking any actions that could aggravate the situation."
The spokesman also denied reports that a son of Kim Jong-il said to be designated as the North Korean leader's successor had paid a visit to China.
A Japanese newspaper, the Asahi Shimbun, reported that North Korean leader Kim Jong-il's youngest son, Kim Jong-un, visited Beijing last week to tell China's leaders that he was his father's chosen successor.
Mr Qin said he was not aware of the reported visit.
Speculation over who would succeed Kim Jong-il mounted after he reportedly had a stroke last year.