To solve the problem that a high-frequency circuit cannot be downsized with a technique wherein an electronic wave absorbing body is attached to a cover, because such a technique causes the height of a case to increase due to the thick electronic wave absorbing body, in a method of reducing propagation of unnecessary electronic waves within the high-frequency circuit.

A cover 8 for a high-frequency circuit 1 has a flat resistor 9, not an electronic wave absorbing body, attached to a surface thereof. The surface of the cover 8 to which the resistor 9 is attached faces circuit elements 5 within a case 2. As a result of this arrangement, current generated in the cover 8 when unnecessary electronic waves propagate through the space within the circuit 1 can be converted into heat by the resistor 9, whereby the unnecessary electronic waves within the circuit 1 can be reduced. Similar advantages can be obtained by a RuO2 resistor film screen-printed on a thick-film cover, and a Ta2N resistor film sputtered on a thin-film cover.