To provide a thin flow-passage forming body constituting a temperature controller that can highly efficiently control temperatures, can be manufactured and attached easily, and can be reduced in size.

This thin flow-passage forming body is provided with first and second sheets, the joining section of the first and second sheets, and a flow passage formed between the first and second sheets. Since either one of the first and the second sheets is provided with at least one heat radiating piece, the thin flow-passage forming body can make heat exchanges with the outside air through the heat radiating piece.