A rotation mechanism is configured to rotate a wafer including an etched region which is to be etched at least partially. An etching mechanism etches the etched region. A thickness measurement function is configured to generate time-dependent thickness data by measuring a thickness of the etched region. An etching control function is configured to stop the etching mechanism when a representative value of thickness of the etched region reaches a target thickness value. A thickness calculation function is configured to calculate the representative value of thickness for each unit period in which the wafer is rotated N times, where N is a natural number, based on measurement values of the time-dependent thickness data in a measurement section being a range measured during the unit period.