Fuente: Wipo "digitalization" A disk apparatus includes buffer memories and a controller for performing control to time-divisionally and alternately write data in two recording areas at different radial positions on an optical disk. Input two-channel digital video data are alternately written in the buffer memories at the bit rate of the video data. The video data stored in the buffer memories are read out at a rate twice the average bit rate or more and written in the optical head by an optical head.