The recent development of SQUID system for biomagnetic study is remarkable. The high sensitive SQUID system makes possible to study the brain function and the research for the application of biomagnetic measurement to the diagnosis is in progress. In this review, the techniques for measuring the weak magnetic fields emanating from active positions in a human body are described and the estimation of source location of the biomagnetic field is described, The SQUID sensor, magnetically shielded room, reduction of magnetic noise and multi-channel SQUID systems are presented.