A signal processing unit (C1, C2, C3) for processing a light reception signal from an imaging element (12) at different magnifications is provided in a light receiving unit (102) in a displacement sensor (1). This sensor (1) measures a displacement by using light receiving amount data generated by the signal processing unit (C1) for each detection processing by a light projecting unit (101) and the light receiving unit (102), and further adjusts sensitivity for next detection processing. In sensitivity adjustment processing, when a peak value in the light receiving amount data generated by the signal processing unit (C1) approximates to 0, a peak value extracted by the signal processing unit (C2) to which higher magnification is applied is employed. Alternatively, when a peak value in the light receiving amount data generated by the signal processing unit (C1) is saturated, a peak value extracted by the signal processing unit (C3) to which 1-fold magnification is applied is employed.