a) forming:

a signal line comprising an input line and an output line formed so that the input line and the output line are aligned and an input line end of the input line is located opposite an output line end of the output line across a predetermined opening portion,

supporting frames on either side of the signal line, and

first and second ground lines, respectively between the supporting frames and the signal line on a substrate;

b) forming:

a sacrificial layer having a predetermined thickness over the surface of the input line, the output line, the supporting frames and the ground lines;

c) forming:

first and second grooves in the sacrificial layer at portions located over the input line end and the output line end, respectively, and then,

forming first and second contact portions in the first and second grooves;

d) forming:

a hole in the sacrificial layer which extends through the sacrificial layer to expose a portion of the substrate between the first and second ground lines,

a support protrusion portion in the hole, and

a supporting layer on the sacrificial layer other than the contact portion;

e) forming a moving plate over the supporting frames and the sacrificial layer and over the supporting layer;

f) forming a switching unit over the supporting layer and the contact portion inside the moving plate; and

g) removing the sacrificial layer.