Japaneseをつかったときは A leading Japanese electronics makerです。A major Japanese Automobile Manufacturerとも使います。Japan'sをつかったときは、Japan's leading steel manufacturersとなります。学校では教えてもらえませんが、基本です。
The four leading Japanese steel manufacturers have reported that they suffered current account deficits during the first half of this business year, but that they have managed to reduce the size of the deficits considerably toward the term end thanks to an increase in exports.
A leading Japanese electronics maker, Toshiba, says it expects to mark operation profits of about 2 billion yen during the April-September period, thanks to an increase in demand for its semiconductor chips.