A magneto-optical disk reproducing device includes a clock producing circuit, which, on the basis of a reproducing signal from recorded marks recorded in a magneto-optical disk, produces a timing offset from peak positions of the reproducing signal; an A/D converter, which samples the reproducing signal in accordance with the timing, and outputs a reproducing signal quantity; and a short mark signal quantity averaging circuit and a long mark signal quantity averaging circuit, each of which averages a plurality of reproducing signal quantities. When projecting a light beam onto a magneto-optical disk, the magneto-optical disk reproducing device controls light quantity of the light beam on the basis of a ratio between the respective values outputted by the foregoing averaging circuits. By this means, the A/D converter is able to sample the reproducing signal at more timings than when a reproducing signal is detected at peak positions thereof, and the magneto-optical disk reproducing device can detect the foregoing ratio more precisely. Consequently, the magneto-optical disk can control the light quantity of the light beam more accurately.