An optimum performance is achieved relative to write-once type optical recording mediums on which information is recorded by means of a blue-violet semiconductor laser. An optical disc recording/reproduction apparatus 10 comprises an LD control section 17 adapted to control the irradiation power of a laser when writing data. If the cycle of the channel clock is T, when forming a recording mark having a length of n.times.T (n being an integer not smaller than 2), a pulse beam is irradiated onto the write-once type information recording medium for n/2 times (decimals, if any, being to be rounded down). When forming a recording mark having a length of not smaller than 6T and even number times of T, a pulse beam is irradiated for n/2 times with all the intermediate pulse beams synchronized with the phase of the channel clock except the leading pulse beam and the tail end pulse beam. When forming a recording mark having a length of not smaller than 6T and odd number times of T, a pulse beam is irradiated with all the intermediate pulse beams delayed from the phase of the channel clock by T/2 except the leading pulse beam and the tail end pulse beam.