A body-carried device includes a receiving bag, two carrying straps, and a heat dissipation system on the backside of the receiving bag. The heat dissipation system has a pump and an airflow guide tube unit. When a user's lower back directly contacts and pushes the pump, the air in the pump is pushed into the main tube and branch tube of the airflow guide tube unit. Some of the air exits the body-carried device through the main tube while the remainder of the air enters the heat dissipation area of the receiving bag through the branch tube. When the user's lower back moves away from the pump, the pump is elastically restored in shape to draw ambient air through the airflow guide tube unit into the pump.