A heat exchanger includes a first tank and a second tank, an inlet and an outlet each connected to either the first tank or the second tank, and a plurality of panel units provided between and connected to the first and second tanks. Each of the panel units has a plurality of tube portions formed as fluid paths and a plurality of plate portions connecting adjacent tube portions and having a thickness less than a thickness of the tube portions. The heat exchanger is lightweight, can be easily assembled and can have a high efficiency in heat exchange.