1. A pharmaceutical composition which comprises as an active ingredient at least one member selected from the group consisting of 3,6-anhydrogalactopyranose represented by formula I: an aldehyde and a hydrate thereof, and 2-O-methylated derivatives of the 3,6-anhydrogalactopyranose, the aldehyde and the hydrate; and a soluble saccharide containing the compound at its reducing end, 2. The pharmaceutical composition according to claim 1, wherein the saccharide is a product produced by acid decomposition under acidic conditions below pH 7 and/or enzymatic digestion of a substance containing at least one compound selected from the group consisting of 3,6-anhydrogalactopyranose represented by formula 1, an aldehyde and a hydrate thereof, and 2-O-methylated derivatives of the 3,6-anhydrogalactopyranose, the aldehyde and the hydrate. 3. The pharmaceutical composition according to claim 2, wherein the substance containing at least one compound selected from the group consisting of 3,6-anhydrogalactopyranose represented by formula 1, an aldehyde and a hydrate thereof, and 2-O-methylated derivatives of the 3,6-anhydrogalactopyranose, the aldehyde and the hydrate is at least one substance selected from the group consisting of agar, agarose and carrageenan. 4. The pharmaceutical composition according to any one of claims 1 to 3, wherein the saccharide is at least one saccharide selected from the group consisting of agarobiose, agarotetraose, agarohexaose, agarooctaose, kappa -carabiose and beta -D-galactopyranosyl-3,6-anhydro-2-O-methyl-L-galactose. 5. The pharmaceutical composition according to any one of claims 1 to 4, having an apoptosis-inducing activity, antiproliferative activity, a carcinostatic activity, an anti-allergic activity, a carcinostatic activity an immunoregulatory activity and inhibiting an activity of lipid peroxide radical production, an activity of inhibiting NO production and an activity of melanin production. 6. Use the pharmaceutical composition according to any one of claims 1 to 4 for the treatment or prevention of carcinomatous diseases, and diseases that require immunoregulation, induction of apotosis, inhibition of lipid peroxide radical production, inhibition of active oxygen production, inhibition of nitric monoxide production. 7. A food which comprises at least one compound according to one of claims 1 to 5. 8. The food according to claim 7 which is a drink. 9. Use of the food according to claims 7-8 for easing disease state or preventing of carcinomatous diseases and diseases that require immunoregulation, induction of apotosis, inhibition of lipid peroxide radical production, inhibition of active oxygen production, inhibition of nitric monoxide production. 10. Use at least one compound selected from the group consisting of 3,6-anhydrogalactopyranose represented by formula I, an aldehyde and a hydrate thereof, and 2-O-methylated derivatives of the 3,6-anhydrogalactopyranose, the aldehyde and the hydrate; and a soluble saccharide containing the compound at its reducing end, in preparation of a pharmaceutical composition for treating and preventing of carcinomatous diseases and diseases that require immunoregulation, induction of apotosis, inhibition of lipid peroxide radical production, inhibition of active oxygen production, inhibition of nitric monoxide production. 11. Use at least one compound selected from the group consisting of 3,6-anhydrogalactopyranose represented by formula I, an aldehyde and a hydrate thereof, and 2-O-methylated derivatives of the 3,6-anhydrogalactopyranose, the aldehyde and the hydrate; and a soluble saccharide containing the compound at its reducing end, in preparation of a food or drink for easing disease state or preventing of carcinomatous diseases and diseases that require immunoregulation, induction of apotosis, inhibition of lipid peroxide radical production, inhibition of active oxygen production, inhibition of nitric monoxide production.