A displacement sensor comprising a sensor head and a controller either integrally or separately; the sensor head comprising: a measurement light emitting optical system for emitting measurement light onto a measurement position of a measurement object from a prescribed angle; an image acquiring optical system (127a, 128) for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an angle different from that of the measurement light emitting optical system; and a two dimensional imaging device for photoelectrically converting an image obtained by the image acquiring optical system (127a, 128) into a video signal corresponding to the image; characterized in that the controller being adapted to control an imaging condition associated with a brightness of the image in the form of the video signal, and to operate under a measurement mode and an observation mode; when the controller operates under the measurement mode, with a light source for measurement turned on, the imaging condition being adjusted in such a manner that a measurement light radiated light image can be imaged at an appropriate brightness but a surrounding part of the measurement object is substantially darker than the appropriate brightness, and a desired displacement being computed according to the video signal obtained by the two dimensional imaging device; when the controller operates under the observation mode, the imaging condition being adjusted in such a manner that the measurement position and the surrounding part of the measurement object can be imaged both at an appropriate brightness, and an image of the measurement position on the surface of the measurement object and the surrounding region being displayed on the screen of an image monitor according the video signal obtained by the two dimensional imaging device. a measurement light emitting optical system for emitting measurement light onto a measurement position of a measurement object from a prescribed angle; an image acquiring optical system (127a, 128) for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an angle different from that of the measurement light emitting optical system; and a two dimensional imaging device for photoelectrically converting an image obtained by the image acquiring optical system (127a, 128) into a video signal corresponding to the image; characterized in that the controller being adapted to control an imaging condition associated with a brightness of the image in the form of the video signal, and to operate under a measurement mode and an observation mode; when the controller operates under the measurement mode, with a light source for measurement turned on, the imaging condition being adjusted in such a manner that a measurement light radiated light image can be imaged at an appropriate brightness but a surrounding part of the measurement object is substantially darker than the appropriate brightness, and a desired displacement being computed according to the video signal obtained by the two dimensional imaging device; when the controller operates under the observation mode, the imaging condition being adjusted in such a manner that the measurement position and the surrounding part of the measurement object can be imaged both at an appropriate brightness, and an image of the measurement position on the surface of the measurement object and the surrounding region being displayed on the screen of an image monitor according the video signal obtained by the two dimensional imaging device.