A coil apparatus including a winding, a bobbin around which the winding is wound, and a terminal fitting connected with the winding. The engage-target tip is pressed in the mounting direction of the unit, thus the engage-target tip retreats from a locking position, where a latching pin is locked so as not to disengage, to a retreat position, where the latching pin can engage with the engage-target portion. The heating module includes a first electrode, a second electrode and a heating element. Further, in the annealing step, in the high-temperature melting layer 3B, platinum particles are melted, rendering the adhesion and diffusion-preventive effect. The at least one processor may also enable determining, whether the particular frequency includes an on-frequency channel based on the determined frequency error. The protective layer is formed by a catalytic chemical vapor deposition on a surface of the resin structure in which the liquid discharge port is opened.