PURPOSE: To provide a communication system unit, in which a plurality of unit components in a frame is protected from external electromagnetic waves, and the unit components are cooled by air effectively.

CONSTITUTION: A unit device 60 with a mother board 62 on the rear face thereof is put vertically in a frame 50 and cooled inside by an air flow from a bottom thereof, and the air is discharged to a ceiling face. Then, the air from the ceiling face is discharged through a duct 70 from the rear face of the frame 50. The rear face of the frame 50 is covered with a conductive rear plate 52 having only an opening 523 for the duct 70.