Japan wants Britain's exit from the European Union to be predictable and transparent so that a senior government official said on Monday.
Deputy Chief Cabinet Secretary Yasutoshi Nishimura said the government would do its utmost to gather information on the Brexit negotiations, which he said remain "fluid", as well as support Japanese corporate activity there.
He made the remarks at a government task force meeting on Britain's exit from the EU.
British Prime Minister Theresa May will visit Japan later this week to discuss Brexit, trade and defense with Premier Shinzo Abe. The visit is aimed at strengthening Britain's relationship with key international investors ahead of the split.
Since the shock Brexit vote, Japan has expressed unusually strong public concerns about the impact of Brexit on the United Kingdom, the second most important destination for Japanese investment after the United States.
"The Japanese government must react to a sense of crisis among businesses and do the utmost to gather information and analyze it, and support Japanese firms based on the recognition that Britain's exit from EU has a direct impact on them," Nishimura said.
"We need to make use of Prime Minister May's visit for conveying Japan's stance to various levels (of officials) in Britain and EU."
Abe has expressed concerns about possible overnight changes in regulations when the country withdraws from the EU in March 2019.
Since voting to leave the EU June last year, Britain has trumpeted decisions by Japanese carmakers Nissan and Toyota to continue production in the country as a sign that Brexit will not scare off global investors.
But both those investments came after the government wrote letters to ease the firms' concerns, drawing criticism that May was making secret deals and giving firms privileged information on Brexit. Britain said the letters were commercially sensitive.
Britain will return to Brexit talks on Monday after it sought to widen the debate by publishing a series of papers in the last two weeks on subjects ranging from future customs arrangements to data.