An optical disk is equipped with a predetermined mark. A frequency generator outputs an FG pulse of frequency corresponding to the rotational speed of a spindle motor used for rotationally driving the optical disk. The edge of the FG pulse detected by an edge detection section is counted by an FG counter. An angle counter measures the duration of a time from appearance of an edge of the FG pulse until a point in time when the mark affixed to the optical disk 1 is detected. A count value of the FG counter, which has been acquired at the point in time when the mark is detected, and a count value of the angle counter are saved. In a case where a visible image is rendered, encoding of a visible image to be rendered is started when the count value of the FG counter and the count value of the angle counter have become equal to the respective saved values.