In an optical disk including at least a rewritable phase change material and comprising a recording layer having a reflectivity of more than 15%, an address output value as an address pit signal component occupying in a reproduced signal in a non recording state is prescribed to be 0. First, an initial bus width and an initial bus frequency of a bus coupled between a CPU and a Northbridge are set, such that the bus operates at the initial bus width and the initial bus frequency. The method further comprises forming, after forming the doped regions, strained semiconductor regions in the recesses, wherein a junction between each doped region and the semiconductor layer is formed below an interface between a strained semiconductor region and the semiconductor layer. In this manner, a large amount of data can be processed at high speed regardless of the contents of operation or data bit width. , Tsn, the brightness of light emitted by the EL elements during at least one sustain period is set to be always lower than the brightness of light emitted by the EL elements during the other sustain periods, and the sustain periods are extended by the amount that the brightness has dropped.