Parallel capacitors (5c and 5d) of impedance matching circuits (5) which are connected to two transistors (1), respectively, have their first ends connected to a ground through via holes (5e and 5f) that are used in common, respectively. Although a conventional circuit necessitates via holes by the number equal to the number of stages multiplied by the number of cells of the transistors (1) for an LPF type impedance matching circuit (3), the present circuit can halve the number of via holes of the LPF type impedance matching circuit (5), thereby being able to downsize the circuit.