A phase-change recording material on which high speed recordingerasing is possible, which has excellent recording characteristics, which has a high storage stability of recording signals and which is excellent in the repeated recording durability, and an information recording medium using the above material are provided. For example, by measuring the circumferential length prior to the shot peening treatment and determining the condition of the shot peening treatment on the basis of the measured length, andor by measuring the circumferential length during the shot peening treatment and terminating the shot peening treatment on the basis of the measured length. When the second situation is detected, the differential PWM signal including a plurality of pulses each having a gradually reduced width and the subsequent pulse train of no signal is generated and, at the same time, the generated pulses are sent to the amplifier via the multiplexer. The improved techniques do not require any human intervention. The sample unit is used for outputting the photovoltage in respond to a sample signal, the sample unit comprising a fourth transistor in respond to the sample signal and a second conversion unit that transforms the output of the fourth transistor into the photovoltage.