Japan Railways (JR Group) is the successor of the national JNR (Japanese National Railways), which was privatized in 1987 due to huge debts.
The JR Group is made up of six regional passenger railway companies:
(photo from Wikipedia used and modify under GNU licence)
and one nationwide freight railway company (JR Freight). Together they operate a nationwide network of urban, regional and interregional train lines, night trains and bullet trains (shinkansen).
The Japanese trains feature two different types of gauge. The first, similar to the european type, measures 1435mm and is mainly used for High Speed trains (Shinkansen), while the more common second type measures 1067mm.
The Japanese N scale due to a different gauge is not 1/160 therefore 1/150
