Patent ID: 7495524

Claim:
An impedance matching apparatus, disposed between a high-frequency power source for outputting a high-frequency power and a load, for matching an impedance of the high-frequency power source and an impedance of the load, the apparatus comprising: a matching unit that includes at least one variable impedance element in which an impedance can be varied by changing a position of a movable portion; a driving unit that is disposed for each of the variable impedance element and changes the position of the movable portion of the variable impedance element in plural steps within a movable range; a controlling unit that varies the impedance of the variable impedance element by controlling the driving unit, thereby matching the impedance of the high-frequency power source and the impedance of the load; an input power acquiring unit that detects or calculates a power value at an input terminal of the matching unit, and outputs the power value as an input power value; a storing unit that previously stores allowable power values respectively corresponding to intended positions in an associated manner with the positions of the movable portion, while, in a case where the matching unit includes one variable impedance element, plural positions which can be taken by the movable portion of the variable impedance element are intended, and, in a case where the matching unit includes plural variable impedance elements, combined positions of plural positions which can be taken by respective movable portions of the plural variable impedance elements are intended; and an abnormality determining unit that sets, based on a present position of the movable portion and the allowable power values stored in the storing unit, an allowable power value corresponding to the present position of the movable portion, compares the allowable power value with the input power value, and that when the input power value is larger than the allowable power value, determines that it is abnormal and outputs an abnormality signal.