To provide a heating device having a good thermal efficiency and capable of reducing manufacturing costs by reducing the number of parts, a heating device mounting structure for mounting the heating device, and an optical waveguide device.

A lead terminal 118 attached on a heating element 117 mounting a heating element not shown, is fixed to a wiring pattern not shown in the figure on a printed circuit board 141 by solder or the like. By the folded strut portion of the lead terminal 118, a gap is provided between the heating device 117 and the printed circuit board 141. Onto the heating element 117, a waveguide element 112 is adhered with adhesive 134. The lead terminal 118 has both roles of carrying electricity and fixing a waveguide device 111. Between the heating element 117 and the printed circuit board 141, an air layer for insulating heat exists, whereby heating of the waveguide element 112 can be efficiently performed.