To provide a heat exchanger excellent in thermal conductivity and having a high withstanding temperature in which repair or inspection can be facilitated while decreasing external profile.

A rotator 11 internally arranged with a heat retaining material 20 ventilating in the axial direction is rotated. A first gas on one side of the rotator 11 is passed to the other side thereof and a second gas is passed in the axial direction thereof thus exchanging heat between first and second gases. In such a heat exchanger, the heat retaining material 20 employs cotton-like metal fibers excellent in thermal conductivity and the cotton-like metal fibers are contained while being divided into a plurality of blocks in the circumferential direction.