The present invention provides a dihydropyridazine-3,5-dione derivative or a salt thereof, or a solvate of the compound or the salt, a pharmaceutical drug, a pharmaceutical composition, a sodium-dependent phosphate transporter inhibitor, and a preventive and/or therapeutic agent for hyperphosphatemia, secondary hyperparathyroidism, chronic renal failure, chronic kidney disease, and arteriosclerosis associated with vascular calcification comprising the compound as an active ingredient, and a method for prevention and/or treatment.
