Prime Minister David Cameron spoke by telephone with the Japanese Prime Minister Shinzō Abe.
A Downing Street spokesperson said:
"The Japanese Prime Minister Shinzō Abe called the Prime Minister earlier this afternoon to thank him for his friendship and support and to wish him well following the referendum.
"They agreed the relationship between the UK and Japan had gone from strength to strength in recent years, and would continue to do so. Our countries had much in common, sharing values and working together in pursuit of global peace and prosperity.
"The Prime Minister said the UK greatly valued the investment of Japanese businesses into the UK, and we would do everything we could to promote and safeguard that investment in the wake of the referendum. It would be important for Japanese companies to make their voices heard in the negotiations once they got under way.
"The Prime Minister said we remained a member of the European Union until negotiations to leave had concluded, and we would continue to support a swift conclusion to the EU-Japan Free Trade Agreement."
Source: Gov.uk (Contains public sector information licensed under the Open Government Licence v3.0.)