British Prime Minister David Cameron's promise to renegotiate Britain's role in the EU and hold a referendum on EU membership by 2017 has already been greeted with concern by the United States among others.
A senior official in Barack Obama's administration said in January that the United States needed London to retain a "strong voice" within the EU, and last week British Foreign Secretary William Hague said that withdrawal from the EU would deter investors, undermine trade and damage Britain's global status.
Japan submitted its statement to a review ordered by Cameron into the balance of power between London and Brussels. The submission highlighted that more than 1,300 companies have invested in Britain, creating 130,000 jobs.
"The advantage of the UK as a gateway to the European market has attracted Japanese investment. The Government of Japan expects the UK to maintain this favourable role," a statement on Japan's British embassy website said.
"The [Japanese] government is committed to making its relationship with the EU stronger than ever before. In this context, it expects that the UK will maintain a strong voice and continue to play a major role in the EU."
In 2011 Japan ranked as the ninth-largest foreign investor in Britain and fourth-largest excluding EU states. Official data showed the stock of Japanese investment in Britain was worth 31 billion pounds (€36 billion).
Japanese companies Toyota and Nissan manufacture cars in Britain and this month Hitachi won a 1.2 billion pound (€1.4 billion) contract to build 270 train carriages in the north of England.