In a small-sized fluid heat exchanging apparatus that heats or cools a huge amount of gas or liquid, a structure makes fluid having a high flow speed impinge perpendicularly against a wall. A flow passage is divided into a high-speed flow passage and a low-speed flow passage, and the high-speed flow passage and the low-speed flow passage are arranged so as to intersect perpendicularly with each other, according to guidelines for the shape of the flow passage. A flow passage designed according to the guidelines provides highly-efficient heat exchange.