An impedance matching apparatus 3 calculates a forward wave voltage Vfo and a reflected wave voltage Vro at an output terminal 3b, based on a forward wave voltage Vfi and a reflected wave voltage Vri at an input terminal 3a, on information on variable values of variable capacitors VC1, VC2 acquired in advance through measurement, and on a T parameter of the impedance matching apparatus 3 corresponding to the information on the variable values of variable capacitors VC1, VC2. The impedance matching apparatus 3 calculates an input reflection coefficient Γi at the input terminal 3a corresponding to the information on the variable values of the variable capacitors VC1, VC2, based on the forward wave voltage Vfo, the reflected wave voltage Vro and the T parameter. The impedance matching apparatus 3 selects the lowest absolute value out of absolute values |Γi| of the input reflection coefficients corresponding to the variable values of the variable capacitors VC1, VC2, and adjusts the impedance of the variable capacitors VC1, VC2 based on the lowest value.