A transistorized B-H loop tracer was constructed in order to suppress the noises from the power supplies and the heater supplies. The C-R coupled integrator was employed to reduce the flicker noises from transistors. By use of the B-H loop circuits, the asteroid curve of magnetic thin films, which defines the switching threshold, as a function of longitudinal and transversal magnetic fields, was automatically traced on the oscilloscope. The switching signals picked up were amplified to have a constant maximum voltage and they were put into the Z-axis of an oscilloscope. This circuit is newly designed by use of the grid control tubes and the brightness on the screen indicates the waveforms of each signal on each point of the asteroid.