rectangular coordinate systems are defined as illustrated in the figures it is to be noted that the md 100 md turntable 200 cd 300 and cd turntable 400 are the same as those of the conventional examples regarding the md turntable 200 and the cd turntable 400 the disc receiving section 3 of the md turntable 200 is displaced by 0 8 mm from the disc receiving section 13 of the cd turntable 400 negatively in the z axis direction the md turntable 200 is set sufficiently apart from the cd turntable 400 in the x axis direction by such a distance that the cd 300 does not interfere with the md turntable 200 when the cd 300 is loaded on the cd turntable 400 an md spindle motor m1 is provided with an md turntable having an md disc receiving section at an end of its rotary shaft and a cd spindle motor m2 is arranged so that its rotary shaft is approximately in parallel with the rotary shaft of the md spindle motor and provided with a cd turntable having a cd receiving section at the rotary shaft end at which the md turntable is provided it is assumed that the line x x is a straight line in parallel with the x axis that connects the center of the md turntable 200 and the center of the cd turntable 400 reference numeral 51 denotes an objective lens which is arranged on the line x x at the side of the light receiving surface of the md 100 or the cd 300 and has at least a function of applying a laser beam onto the data recording surface of the md 100 or the cd 300 reference numeral 50 denotes an optical head.