The present invention provides a means capable of determining the surface state of the target to execute accurate and quick cleaning of necessary part. The means includes: a magnet unit capable of forming a magnetic field on the surface of a target; a rotary system capable of driving the magnet unit of change the magnetic field pattern; and an ammeter configured to measure target current when the magnetic field is formed by the magnet unit and discharge voltage is applied to a target electrode to which the target is attached. The position of the magnet unit is variously changed by the rotary system, and the target current is measured at each position and compared with a reference value. It is then determined whether cleaning is necessary at each position, so that cleaning can be performed only for necessary part.