The present invention relates to an exhaust gas treatment device (4) and an exhaust system (1) having such an exhaust gas treatment device (4), wherein the exhaust system (1) has at least one exhaust-gas-conducting exhaust gas feed line (2, 3), which is attached to an inlet region (16) of the exhaust gas treatment device (4). Improved mixing of the exhaust gas and a space-saving configuration result if the exhaust gas treatment device (4) has at least one inlet (12, 13) which is open towards the inlet region (16) and if a mixing element (15) is provided, which connects the inlet region (16) to a through-flow region (17) by means of input openings (22, 23), wherein at least one first input opening (22) faces a first side (18) of the inlet region (16) and at least one second input opening (23) faces a second side (19) of the inlet region (16).