The invention provides magnesium fuel cells which can prevent the self-discharge of negative electrode materials and can produce electricity stably for a long term. A magnesium fuel cell includes a negative electrode material including a magnesium alloy, and an electrolytic solution for eluting magnesium ions from the negative electrode material. The magnesium alloy contains aluminum and calcium. The electrolytic solution is preferably an aqueous sodium chloride solution, an aqueous sodium hydroxide solution, an aqueous sodium hydrogencarbonate solution, an aqueous sodium percarbonate solution, or a mixture including two or more of these solutions.