To provide a heat exchanger having a simple structure that can efficiently perform heat exchange.

This high-speed heat exchanger 1 has a circulating passage 8 for water to be heated formed in a cylindrical heat exchanger case 5. In the case 5, a rotary heat radiating unit 10 which is rotationally driven at a high speed by means of a rotationally driving mechanism 50 is coaxially arranged. In the heat radiating unit 10, a plurality of branch tubes 14, 15, and 16 forming circulating passages for circulating heat source water are connected. Since heat exchange is performed while the heat radiating unit 10 is rotated, highly efficient heat exchange is realized.