A position detection unit (12) calculates, as a first phase, the deflection angle of a first similarity vector having as elements a first similarity and a second similarity calculated by a similaritycalculation unit (11). The position calculation unit (12) calculates, as a second phase, the deflection angle of a second similarity vector having as elements a third similarity and a fourth similarity calculated by the similarity calculation unit (11). A period calculation unit (13) calculates the period of a pattern formed on a long body on the basis of the first phase and second phase calculated by the phase calculation unit (12). An abnormality detection unit (14) detects an abnormality in the long body on the basis of the period calculated by the period calculation unit (13).