An intake system (50, 250) of an internal combustion engine (100, 200) with a supercharger comprising: a negative pressure control valve (32,232) which is disposed in the upstream side than an intake side supercharger in an intake passage; a first external gas introduction passage which introduces a single external gas made of blow-by gas, at a part of the intake passage which is on the upstream side of the intake side supercharger and on the downstream side of the negative pressure control valve: a fresh air introduction passage which introduces fresh air to an internal combustion engine main body from the upstream side of the negative pressure control valve; and a second external gas introduction passage which is provided separately from the first external gas introduction passage, and introduces another external gas different from the blow-by gas to the part of the intake passage which is on the upstream side of the intake side supercharger and on the downstream side of the negative pressure control valve, characterized in that the single external gas made of the blow-by gas is introduced to the intake passage from a negative pressure region generated on the downstream side of the negative pressure control valve and the vicinity thereof via the first external gas introduction passage, the first external gas introduction passage and the second external gas introduction passage are provided at the same height position in a state where the first external gas introduction passage and the second external gas introduction passage are opposed to each other, and the negative pressure control valve (32, 232) has a predetermined angle with respect to a line segment extending in the intake flow direction from the shaft center of the negative pressure control valve (32, 232) and abuts against the first external gas introduction passage and the second external gas introduction passage when the negative pressure control valve (32, 232) is controlled to be completely opened. a negative pressure control valve (32,232) which is disposed in the upstream side than an intake side supercharger in an intake passage; a first external gas introduction passage which introduces a single external gas made of blow-by gas, at a part of the intake passage which is on the upstream side of the intake side supercharger and on the downstream side of the negative pressure control valve: a fresh air introduction passage which introduces fresh air to an internal combustion engine main body from the upstream side of the negative pressure control valve; and a second external gas introduction passage which is provided separately from the first external gas introduction passage, and introduces another external gas different from the blow-by gas to the part of the intake passage which is on the upstream side of the intake side supercharger and on the downstream side of the negative pressure control valve, characterized in that the single external gas made of the blow-by gas is introduced to the intake passage from a negative pressure region generated on the downstream side of the negative pressure control valve and the vicinity thereof via the first external gas introduction passage, the first external gas introduction passage and the second external gas introduction passage are provided at the same height position in a state where the first external gas introduction passage and the second external gas introduction passage are opposed to each other, and the negative pressure control valve (32, 232) has a predetermined angle with respect to a line segment extending in the intake flow direction from the shaft center of the negative pressure control valve (32, 232) and abuts against the first external gas introduction passage and the second external gas introduction passage when the negative pressure control valve (32, 232) is controlled to be completely opened. a fresh air introduction passage which introduces fresh air to an internal combustion engine main body from the upstream side of the negative pressure control valve; and a second external gas introduction passage which is provided separately from the first external gas introduction passage, and introduces another external gas different from the blow-by gas to the part of the intake passage which is on the upstream side of the intake side supercharger and on the downstream side of the negative pressure control valve, characterized in that the single external gas made of the blow-by gas is introduced to the intake passage from a negative pressure region generated on the downstream side of the negative pressure control valve and the vicinity thereof via the first external gas introduction passage, the first external gas introduction passage and the second external gas introduction passage are provided at the same height position in a state where the first external gas introduction passage and the second external gas introduction passage are opposed to each other, and the negative pressure control valve (32, 232) has a predetermined angle with respect to a line segment extending in the intake flow direction from the shaft center of the negative pressure control valve (32, 232) and abuts against the first external gas introduction passage and the second external gas introduction passage when the negative pressure control valve (32, 232) is controlled to be completely opened.