An eddy current sensor (10) has a sensor coil (100) disposed near a conductive film (6) formed on a semiconductor wafer (W) and a signal source (124) configured to supply an AC signal to the sensor coil (100) to produce an eddy current in the conductive film (6). The eddy current sensor (10) includes a detection circuit operable to detect the eddy current produced in the conductive film (6). The detection circuit is connected to the sensor coil (100). The eddy current sensor (10) also includes a housing (200) made of a material having a high magnetic permeability. The housing (200) accommodates the sensor coil (100) therein. The housing (200) is configured so that the sensor coil (100) forms a path of a magnetic flux (MF) so as to effectively produce an eddy current in the conductive film (6).