A gypsum dewatering device 2 installed in a desulfurization facility 105 in which sulfur oxide in flue gas G is absorbed by limestone in an absorber 1, includes a belt filter 22 that absorbs sulfur oxide and dewaters gypsum slurry SS fed from the absorber 1 to form a gypsum cake SC, a vacuum suction mechanism 23 that sucks moisture in the gypsum cake SC via the belt filter 22, a moisture measuring means H1 that measures a moisture content of the gypsum cake SC to be dewatered by the belt filter 22, a heating means 25 that heats the gypsum cake SC dewatered by the belt filter 22 by hot water or steam, and a control means 26 that controls a heated state by the heating means 25 when the moisture content of the gypsum cake SC input from the moisture measuring means H1 has exceeded a predetermined amount.