We described a method for measuring 3D position and orientation of endoscopic probe using magnetic field. We derived particularly three expressions of magnetic field generated respectively by three mutually orthogonal coils, and also derived three expressions of the magnetic induction signals obtained by three mutually orthogonal magnetic field sensors attached to the endoscope. Then we constructed 6D nonlinear equation group (including 3D positions and 3 attitude angles), and adopted Newton Laferson arith...