Evaluation of aging structural health relies on the high skill of non-destructive testing technicians. This study proposes a method to quantify the skill of non-destructive testing technicians. The target of non-destructive testing is eddy current testing. A skill evaluation system comprises a probe, a data acquisition unit and a laptop computer. The system records the signal voltage at 500Hz while a technician operates the probe and tests an object. First, the proposed method classified the voltage into five states. Second, the rate of one-step state transitions was calculated from the state data. Third, using template data based on the state transition data of qualified technicians, the difference between the template and experimental data was quantified as an evaluation value. Through an experiment with six subjects, we verified that the evaluation value quantified the difference between qualified and unqualified skills.