An NOx reduction control method for an exhaust gas aftertreatment device having an oxidation catalyst and an LNT catalyst which are disposed in an exhaust pipe and repeating an adsorption or occlusion of NOx which is executed when an air-fuel ratio is in a lean state and a reduction of NOx which is executed when the air-fuel ratio is in a rich state, wherein the LNT catalyst is disposed downstream of the oxidation catalyst, and the oxidation catalyst adsorbs HC when an exhaust gas temperature is lower than a catalyst activation temperature, and desorbs HC adsorbed when the exhaust gas temperature is equal to or greater than the catalyst activation temperature, the method comprising: executing a post-injection of fuel or an exhaust pipe injection of fuel and causing HC to be adsorbed in the oxidation catalyst when an exhaust gas temperature is lower than a catalyst activation temperature; estimating an HC adsorption amount adsorbed in the oxidation catalyst; stopping the post-injection or the exhaust pipe injection when the HC adsorption amount reaches a threshold value; and after HC is adsorbed in the oxidation catalyst, causing the HC which is adsorbed in the oxidation catalyst to be desorbed and reducing an adsorbed NOx in the LNT catalyst by raising the exhaust gas temperature when the exhaust gas temperature exceeds the catalyst activation temperature and it is instructed that the air-fuel ratio is caused to be in the rich state based on an amount of the adsorbed NOx. wherein the LNT catalyst is disposed downstream of the oxidation catalyst, and the oxidation catalyst adsorbs HC when an exhaust gas temperature is lower than a catalyst activation temperature, and desorbs HC adsorbed when the exhaust gas temperature is equal to or greater than the catalyst activation temperature, the method comprising: executing a post-injection of fuel or an exhaust pipe injection of fuel and causing HC to be adsorbed in the oxidation catalyst when an exhaust gas temperature is lower than a catalyst activation temperature; estimating an HC adsorption amount adsorbed in the oxidation catalyst; stopping the post-injection or the exhaust pipe injection when the HC adsorption amount reaches a threshold value; and after HC is adsorbed in the oxidation catalyst, causing the HC which is adsorbed in the oxidation catalyst to be desorbed and reducing an adsorbed NOx in the LNT catalyst by raising the exhaust gas temperature when the exhaust gas temperature exceeds the catalyst activation temperature and it is instructed that the air-fuel ratio is caused to be in the rich state based on an amount of the adsorbed NOx. executing a post-injection of fuel or an exhaust pipe injection of fuel and causing HC to be adsorbed in the oxidation catalyst when an exhaust gas temperature is lower than a catalyst activation temperature; estimating an HC adsorption amount adsorbed in the oxidation catalyst; stopping the post-injection or the exhaust pipe injection when the HC adsorption amount reaches a threshold value; and after HC is adsorbed in the oxidation catalyst, causing the HC which is adsorbed in the oxidation catalyst to be desorbed and reducing an adsorbed NOx in the LNT catalyst by raising the exhaust gas temperature when the exhaust gas temperature exceeds the catalyst activation temperature and it is instructed that the air-fuel ratio is caused to be in the rich state based on an amount of the adsorbed NOx. <EOS>