A displacement measuring device capable of accurately measuring a distance to a measurement target surface is provided. The displacement measuring device includes a light projecting part generating light, a sensor head irradiating a measurement target with the light and receiving light of the irradiated light reflected by a measurement target surface of the measurement target, and a control part calculating a value indicating a distance to the measurement target surface on the basis of the light received by the sensor head. The control part processes the calculated value as the value indicating the distance to the measurement target surface on condition that the calculated value is included in a preset numerical range and resets the preset numerical range on the basis of the calculated value.