Abstract: An intracellular calcium concentration increase inhibitor containing as the active ingredient (1) a boron compound represented by the formula (I). The compound represented by the formula (I) inhibits the increase of the intracellular calcium concentration, and therefore it is deemed to be useful as an agent for the prophylaxis and/or treatment of platelet aggregation, ischemic diseases in hearts and brains, immune deficiency diseases, allorgosis, bronchial asthma, hypertension, cerebrovascular spasm, various renal diseases, pancreatitis, Alzheimer's disease, etc.