A NOx sensor diagnosis apparatus that diagnoses a NOx sensor provided in an exhaust pipe of an engine (E) and configured to detect the concentration of NOx in exhaust gas, the apparatus comprising: a calculation value operating unit configured to acquire the calculation value of the concentration of NOx in the exhaust gas based on the actuation state of the engine (E); an error determining unit configured to determine that the NOx sensor is erroneous when a difference between the calculation value of the concentration of NOx acquired by the calculation value operating unit and the detection value of the concentration of NOx detected by the NOx sensor is larger than a determination threshold value; and a determination threshold value setting unit configured to set the determination threshold value based on the temperature of the cooling water for cooling the engine (E); characterized in that the determination threshold value setting unit is configured to set the determination threshold value based on an atmospheric pressure and an outdoor temperature, and in that the error determining unit is configured to determine that the NOx sensor is erroneous when a difference between the calculation value of the concentration of NOx acquired by the calculation value operating unit and the detection value of the concentration of NOx detected by the NOx sensor after the calculation value operating unit acquires the calculation value of the concentration of NOx is larger than a determination threshold value, and the determination threshold value setting unit is configured to set the determination threshold value based on the temperature of the cooling water for cooling the engine, the atmospheric pressure, and the outdoor temperature acquired after the calculation value operating unit acquires the calculation value of the concentration of NOx. a calculation value operating unit configured to acquire the calculation value of the concentration of NOx in the exhaust gas based on the actuation state of the engine (E); an error determining unit configured to determine that the NOx sensor is erroneous when a difference between the calculation value of the concentration of NOx acquired by the calculation value operating unit and the detection value of the concentration of NOx detected by the NOx sensor is larger than a determination threshold value; and a determination threshold value setting unit configured to set the determination threshold value based on the temperature of the cooling water for cooling the engine (E); characterized in that the determination threshold value setting unit is configured to set the determination threshold value based on an atmospheric pressure and an outdoor temperature, and in that the error determining unit is configured to determine that the NOx sensor is erroneous when a difference between the calculation value of the concentration of NOx acquired by the calculation value operating unit and the detection value of the concentration of NOx detected by the NOx sensor after the calculation value operating unit acquires the calculation value of the concentration of NOx is larger than a determination threshold value, and the determination threshold value setting unit is configured to set the determination threshold value based on the temperature of the cooling water for cooling the engine, the atmospheric pressure, and the outdoor temperature acquired after the calculation value operating unit acquires the calculation value of the concentration of NOx. <EOS>