D.C. magnetic hysteresis loop tracer using the digital sampling technique was constructed. This automatic system can measure the hysteresis loop in the extremely low frequency (0.02-0.1 Hz) range. The drift of the fluxmeter observed in the conventional hysteresis loop tracer can be moderately removed by this technique. The advantages of the developed system are as follows. First, it is easier to measure hysteresis loop compared with conventional measuring system. Second, the measured data are stored and displayed by computer.