PURPOSE: To form a heat insulating layer onto the outside surface of a heat exchanger without spattering a foaming liquid, by spraying a foamed heat insulating material onto the outside surface through a tube at the tip of a spray foamer.

CONSTITUTION: A heat exchanger 1 is settled horizontally by a rotary jig 2, and rotated along the direction shown by the arrow. A formed heat insulating material is injected onto the rotating heat exchanger through a tube 3 at the tip of a spray foamer, so that a heat insulating layer is formed on the outside surface of the heat exchanger 1.