A total heat exchanger having a structure capable of achieving an enhancement in total heat efficiency, and a ventilation system using the total heat exchanger are disclosed. The total heat exchanger includes an air supply duct for guiding outdoor air to an indoor space, an air discharge duct for guiding indoor air to the outdoors, an air supply fan arranged at one side of the air supply duct, the air supply fan sucking the outdoor air, and supplying the sucked air to the indoor space, an air discharge fan arranged at one side of the air discharge duct, the air discharge fan sucking the indoor air, and discharging the sucked air to the outdoors, and a heat exchanging element arranged at a region where the indoor air and the outdoor air cross each other, the heat exchanging element heat-exchanging the indoor air with the outdoor air. The heat exchanging element has a shape causing the indoor air and the outdoor air to flow through the heat exchanging element while forming an acute angle with respect to each other.