Shinjuku-nishiguchi Station is served by the Toei Oedo Line, and is numbered "E-01".

The station has one island platform, serving two tracks, located on the 4th basement ("B4F") level.

The north ticket gate leads to various exit points to Oogado Crossing.

The south gate leads to the Odakyu Department store area and the Marunouchi Line.

[1] In fiscal 2011, the station was used by an average of 51,059 passengers daily.