An impedance matching method includes: calculating an output impedance of a theoretical circuit model set in advance from actual values of two variable components and a measured value of an input impedance; calculating values of the two variable components at the time of impedance matching through an arithmetic operation under a matching condition in the theoretical circuit model based on the calculated value of the output impedance assuming that the output impedance due to matching transition has the same value; and controlling the actual values of the variable components of the impedance matching device to correspond to the calculated two variable component values.