A read out means reads out, from a multisession type optical disk which has been loaded, identification information which indicates its type, and a recommended write strategy pulse width. A calculation means, when a decision means has decided that the multisession type optical disk is of an unknown type, calculates a compensated pulse width based upon the value of the difference between the average value of the intrinsic write strategy pulse widths which are stored by a strategy storage means in correspondence with the identification information, and the recommended write strategy pulse width which has been read out by the read out means. And a recording means performs recording of data with laser light which has been modulated to the compensated pulse width as calculated by the calculation means.