Antarctica is a continent characterized by the huge ice mass above the bedrock. Better understanding the internal physical mechanism for existence and changes is essential to study how ice is fixed on the continent in water cycles in the atmosphere-ocean-ice system on the earth. The National Institute of Polar Research, Tokyo, has a long history of using ice sounding radar to study the ice sheet. This paper gives a brief history of the development, specifications, observations and major results. In particular, it explains the use of multiple frequencies and polarization planes. This paper also comments on the recent use of phase information in addition to power information. I hope that this document will be useful for future use of the radar.