An impedance matching device comprises a variable capacitor including multiple capacitance elements and connected in parallel having capacitors and each having one end connected in series to a high-frequency power source and semiconductor switches and connected to the respective capacitors, and a control unit. The control unit derives a reflection coefficient based on the obtained information concerning an impedance viewed from the high-frequency power source toward the load side, updates the states of the respective semiconductor switches and included in the multiple capacitance elements and with a first cycle in the case where the reflection coefficient is equal to or more than a predetermined value, and updates the states of the respective semiconductor switches and included in the plurality of capacitance elements and with a second cycle longer than the first cycle in the case where the reflection coefficient is less than the predetermined value.