Thecover 24 is formed of a metal, such as stainless steel or copper alloy or like material, and may be surface-treated with solder, tin, silver, or a like metal at an appropriate portion in order to improve solderability.The above-mentioned elements of the variable capacitor 21 will next be described in detail.As shown in FIGS. 1 to 4, the stator 22 generally has a symmetrical structure.