Eccentricity tester for head turnout zone of magnetic disk and testing method thereof

The tester and the test method for testing an eccentricity of a head turnout zone of a magnetic disk determine a turnout zone as acceptable or unacceptable by spirally scanning a turnout zone of a magnetic disk with a laser spot by rotating the magnetic disk and continuously moving either the laser spot radially of the magnetic disk or the magnetic disk radially thereof, obtaining a detection signal having amplitude corresponding to an intensity of a scattering light from the magnetic disk irradiated with the laser spot, extracting a first waveform of the detection signal corresponding to an intermediate region between an inside variation region in which an inside boarder line of the turnout zone radially of the magnetic disk by radial movement of the turnout zone caused by an ecentricity of the turnout zone and an outside variation region in which an outside boarder line of the turnout zone radially of the magnetic disk by the radial movement of the turnout zone caused by the eccentricity of the magnetic disk and a second waveform of either the detection signal adjacent to the first waveform and corresponding to the inside variation region or the detection signal adjacent to the first waveform and corresponding to the outside variation region and detecting an eccntricity of the turnout zone on a basis of a positional relation between the first and second waveforms.