Information to be recorded is recorded in a recording layer of a phase-change optical storage medium. The information to be recorded is modulated to generate modulated data. Desired mark-length data is generated based on the modulated data. Generated further based on the mark-length data is a recording pulse pattern of recording pulses rising from an erasing power and formed between a recording power larger than the erasing power and a bottom power smaller than the erasing power and of erasing pulses rising from the bottom power to the erasing power. A recording light beam is then irradiated onto the recording layer in accordance with the recording pulse pattern to record at least one recorded mark representing the information to be recorded. Used in recording is an optimum erasing power, as the erasing power, the optimum erasing power satisfying an expression (1): 1.000<(R1/R0)<1.030 . . . (1) in which R0 is a reflectivity exhibited by an un-recorded section of the recording layer, on which no data has ever been recorded, when irradiated with a reproducing light beam, and R1 is a reflectivity exhibited by the un-recorded section when irradiated with the reproducing light beam after irradiated once with a beam having the erasing power.