The invention provides a multiple gas detection device and a multiple gas detection method, being able to accurately detect the concentration of the components in the detected gas. The multiple gas detection device (1) comprises: a first cell part provided with a first electrochemical cell (51); a second cell part provided with a second electrochemical cell (52); a third cell part provided with a third electrochemical cell (53); an inlet diffusion controller (15) controlling diffusion of measured gas; and a measured gas chamber (30) into which the measured gas flows through the inlet diffusion controller (15). The first cell part is configured to selectively detect a concentration of NO x or ammonia contained in measured gas in the measured gas chamber (30). The second cell part is configured to discharge oxygen contained in measured gas in the measured gas chamber (30) and convert NO 2 and ammonia contained in measured gas in the measured gas chamber (30) to NO. The third cell part is configured to detect a concentration of NO contained in measured gas in the measured gas chamber (30).