PURPOSE: To form an irregular surface at an upper part of a heat collecting sheet, dispose a pipe passage adjacent to the irregular surface, supply thermal medium liquid to a recessed surface of the irregular surface from the pipe passage, thereafter the liquid is overflown from a projection surface and a changing of the thermal medium liquid supplying capability or a manufacturing process is facilitated.

CONSTITUTION: An irregular surface 2 continued in a lateral direction is formed at an upper position of a heat collecting sheet 1. A pipe passage 3 for supplying thermal medium liquid is disposed adjacent to the irregular surface 2 and then thermal medium is supplied from the pipe passage 3 to the irregular surface 2. In addition, the supplied thermal medium liquid is overflown from the projection surface 2a and flowed down along an outer surface of the heat collecting sheet 1. During this operation, the irregular surface 2 is disposed at a top end of the heat collecting sheet 1, the heat collecting sheet 1 itself is deformed. In order to deform the heat collecting sheet 1, a back-up material 6 is mounted. With such an arrangement, a discharged amount of liquid can be simply and positively increased or decreased by adjusting a relative level difference in height at the recessed surface 2b and the projection surface 2a of the irregular surface 2.