In a waveform processing circuit comprising a delay line for delaying a signal outputted from a ring type magnetic head reproducing a perpendicular magnetization recording, an attenuator for attenuating the signal delivered out of the ring type magnetic head, and a differential amplifier for receiving outputs from the delay line and the attenuator, wherein a waveform of the signal is processed to discriminate a position of magnetization transition based on the waveform of the signal; the delay time .tau. of the delay line is selected to satisfyv.multidot..tau..ltoreq.gwhere, v is a relative speed between the recording medium and the magnetic head and g indicates the gap length of the magnetic head.