A displacement measurement device comprising: a light projecting unit configured to generate a light beam ; a sensor head configured to emit the light beam to a measurement target object of which a measured value and an actual displacement are nonlinear so that a focus is formed on a measurement target surface of the measurement target object , and receive a light beam that is reflected at the measurement target surface within the emitted light beam ; a storage unit configured to store a function using a distance between the sensor head and the measurement target surface as a variable; and a control unit configured to calculate the distance based on a wavelength of the light beam received by the sensor head , the displacement measurement device being characterized in that the control unit is configured to calculate a value of the function by using the calculated distance between the sensor head and a measurement target surface of a first measurement target object which is the measurement target object as a value of the variable, and correct the calculated distance using the calculated value of the function by subtracting the calculated value of the function from the calculated distance, the control unit is configured to generate the function on the basis of another distance calculated at each of a plurality of positions of a stage and a reference distance when the another distance is calculated, the control unit is configured to generate the function based on the another distance and a difference between the another distance and the reference distance, and the control unit is configured to divide a numerical value range of the variable in a plurality of sections (Q1-Q6) using the another distance calculated at each of the plurality of positions, and to generate the respective function of each of the plurality of sections (Q1-Q6). a light projecting unit configured to generate a light beam ; a sensor head configured to emit the light beam to a measurement target object of which a measured value and an actual displacement are nonlinear so that a focus is formed on a measurement target surface of the measurement target object , and receive a light beam that is reflected at the measurement target surface within the emitted light beam ; a storage unit configured to store a function using a distance between the sensor head and the measurement target surface as a variable; and a control unit configured to calculate the distance based on a wavelength of the light beam received by the sensor head , the displacement measurement device being characterized in that the control unit is configured to calculate a value of the function by using the calculated distance between the sensor head and a measurement target surface of a first measurement target object which is the measurement target object as a value of the variable, and correct the calculated distance using the calculated value of the function by subtracting the calculated value of the function from the calculated distance, the control unit is configured to generate the function on the basis of another distance calculated at each of a plurality of positions of a stage and a reference distance when the another distance is calculated, the control unit is configured to generate the function based on the another distance and a difference between the another distance and the reference distance, and the control unit is configured to divide a numerical value range of the variable in a plurality of sections (Q1-Q6) using the another distance calculated at each of the plurality of positions, and to generate the respective function of each of the plurality of sections (Q1-Q6). <EOS>