Provided is a method for reducing carbon dioxide, which comprises the following steps (a) and (b). Step (a) is for preparing an electrochemical cell. The electrochemical cell comprises a working electrode (21), a counter electrode (23), and a vessel (28). The vessel (28) holds an electrolyte (27). The working electrode (21) contains at least one nitride selected from titanium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and iron nitride. The electrolyte (27) contains carbon dioxide. The working electrode (21) and the counter electrode (23) make contact with the electrolyte (27). Step (b) is a step for applying negative voltage and positive voltage to the working electrode (21) and the counter electrode (23), respectively, and reducing carbon dioxide.