PURPOSE: To provide a rotary heat accumulative type heat exchanger core in which a heat transfer to a fixed part of a ring gear is reduced so as to improve a heat resistance characteristic.

CONSTITUTION: A ring gear 16 rotatably installed within a case 13 and for transmitting a driving force to an outer circumference of it is attached through an elastomer 28, and this ring gear has heat accumulation parts 17 and 18. A heat exchanger core in which a first supplying passage and a first discharging passage for fluid of low temperature and a second supplying passage 21 and a second discharging passage 22 for fluid of high temperature are connected in constructed such that there is provided a slit 31 acting as a heat insulating part at an upstream side of the fluid of high temperature at the outer circumference to which the ring gear 16 is fixed.