Abstract: An object of the present invention is to provide a miniaturized wireless microphone.

Abstract: A reactance of a reactance element in a multi-layer circuit board apparatus is trimmed by cutting a portion of the circuit pattern of the reactance element with a laser beam. The reactance element is sandwiched between grounded layers. A coil circuit pattern having at least a hole therein may be provided as the reactance element. A side portion between the edge of the coil circuit pattern and the hole is cut with the laser beam to trim the inductive reactance. Cutting is effected while the circuit is operated and the operating condition such as an oscillation frequency is observed. A plurality of holes may be provided in the coil circuit pattern. The trimming amount of the inductive reactance is determined by the number of the hole subjected to cutting. The holes may have different sizes. The trimming amount is obtained by which one of the hole is subjected to cutting. The distance between the cut circuit pattern is equal to or larger than the thickness of the circuit pattern.