A network communication device, wherein: a relay circuit board coupled to a power supply unit is placed in a vertical direction in the middle of a chassis; a plurality of first circuit board units, each of which includes a first semiconductor device, are arranged in a horizontal direction in the chassis at positions closer to a front side of the chassis than the relay circuit board; one or more cooling units equipped with a fan and a plurality of second circuit board units, each of which includes a second semiconductor device, are arranged side by side in the chassis at positions closer to a back side of the chassis than the relay circuit board; and each first circuit board unit, each second circuit board unit, and each cooling unit are coupled to each other via the relay circuit board and electric power from the power supply unit is supplied via the relay circuit board to each first circuit board unit, each second circuit board unit, and each cooling unit; a plurality of first intake holes for introducing intake air to a lateral side of each first circuit board unit are formed in a front face of the chassis and a first exhaust hole for discharging cooling air discharged from the cooling unit to outside of the chassis is formed in a back face of the chassis; a plurality of second intake holes are formed in a front side of each first circuit board unit; a plurality of openings for introducing the intake air, which has been introduced from each of the plurality of second intake holes to around each first circuit board unit, to the cooling unit are formed in the relay circuit board; in the chassis a plurality of first circuit board unit air passages including each second intake hole, a first space part around each first circuit board unit, each opening in the relay circuit board, and a second space part between a back side of the relay circuit board and the cooling unit are formed; and characterized in that a plurality of second circuit board unit air passages (310, 320) including each first intake hole, a third space part between the chassis and a first partition provided on a lateral side of each first circuit board unit, a vent hole formed on the back side of the relay circuit board within the first partition, and a fourth space part between the back side of the relay circuit board and the cooling unit are formed; any of the second circuit board units is placed within each second circuit board unit air passage (310, 320). a relay circuit board coupled to a power supply unit is placed in a vertical direction in the middle of a chassis; a plurality of first circuit board units, each of which includes a first semiconductor device, are arranged in a horizontal direction in the chassis at positions closer to a front side of the chassis than the relay circuit board; one or more cooling units equipped with a fan and a plurality of second circuit board units, each of which includes a second semiconductor device, are arranged side by side in the chassis at positions closer to a back side of the chassis than the relay circuit board; and each first circuit board unit, each second circuit board unit, and each cooling unit are coupled to each other via the relay circuit board and electric power from the power supply unit is supplied via the relay circuit board to each first circuit board unit, each second circuit board unit, and each cooling unit; a plurality of first intake holes for introducing intake air to a lateral side of each first circuit board unit are formed in a front face of the chassis and a first exhaust hole for discharging cooling air discharged from the cooling unit to outside of the chassis is formed in a back face of the chassis; a plurality of second intake holes are formed in a front side of each first circuit board unit; a plurality of openings for introducing the intake air, which has been introduced from each of the plurality of second intake holes to around each first circuit board unit, to the cooling unit are formed in the relay circuit board; in the chassis a plurality of first circuit board unit air passages including each second intake hole, a first space part around each first circuit board unit, each opening in the relay circuit board, and a second space part between a back side of the relay circuit board and the cooling unit are formed; and characterized in that a plurality of second circuit board unit air passages (310, 320) including each first intake hole, a third space part between the chassis and a first partition provided on a lateral side of each first circuit board unit, a vent hole formed on the back side of the relay circuit board within the first partition, and a fourth space part between the back side of the relay circuit board and the cooling unit are formed; any of the second circuit board units is placed within each second circuit board unit air passage (310, 320).