PROBLEM TO BE SOLVED: To provide an optical disk and optical disk unit which can maintain good characteristic of reproducing recording marks even if the number of reproducing (trace) reaches a considerable number. SOLUTION: The optical disk 100 holds a correction coefficient ν in a lead in area. The lead in correction coefficient ν is read out when the optical disk 100 is loaded and stored in an inner memory of a controller 111. In OPC operation, the controller 111 executes trial writing on the optical disk, and obtains a recording laser power Pmax with which PRSNR becomes the best, and further sets up the recording laser power Ppot for the optical disk by multiplying the obtained recording laser power with the correction coefficient ν. The correction coefficient ν corrects the recording laser power Pmax for improving durability to the trace number of the recorded marks so that the recording with the recording laser power Ppot improves durability to the trace number of the recorded marks. COPYRIGHT: (C)2008,JPO&INPIT