An automatic tracking apparatus adapted to track a reflector comprising: a surveying machine body; an illumination portion which is disposed in said surveying machine body and has a laser diode which is adapted to illuminate modulated measurement light toward a reflector; a light receiving portion which is disposed in said surveying machine body and which has an image sensor adapted to receive a reflection light image of the measurement light illuminated toward said reflector; a central processing device as arithmetic means adapted to calculate a position of the reflection light image from said reflector in an area of said image sensor; and a rotation mechanism adapted to rotate said surveying machine body so as to position the reflection light image on a light receiving optical axis of said light receiving portion based on the position obtained by said central processing device, characterized in that said light receiving portion is also provided with a beam splitter and a light receiving sensor, the light receiving sensor and the image sensor disposed in a conjugated position through the beam splitter and the area of the light receiving sensor being smaller than the area of the image sensor, wherein the modulated measurement light is a frequency modulated light and said central processing device is adapted to distinguish the reflection light image from said reflector from a light image other than the reflection light image based on a frequency of an output of said light receiving sensor, wherein the frequency modulated measurement light is pulsed light, and wherein said light receiving portion is further provided with a synchronization detecting circuit adapted to synchronously detect the output of said light receiving sensor based on said frequency modulated pulsed light; wherein the synchronization detecting circuit is adapted to outputs a coincidence signal toward the central processing device when a modulation frequency and a frequency of the output from the light receiving sensor coincide, and the central processing device is adapted to judge that the light image on the optical axis is the light image of the reflector. a surveying machine body; an illumination portion which is disposed in said surveying machine body and has a laser diode which is adapted to illuminate modulated measurement light toward a reflector; a light receiving portion which is disposed in said surveying machine body and which has an image sensor adapted to receive a reflection light image of the measurement light illuminated toward said reflector; a central processing device as arithmetic means adapted to calculate a position of the reflection light image from said reflector in an area of said image sensor; and a rotation mechanism adapted to rotate said surveying machine body so as to position the reflection light image on a light receiving optical axis of said light receiving portion based on the position obtained by said central processing device, characterized in that said light receiving portion is also provided with a beam splitter and a light receiving sensor, the light receiving sensor and the image sensor disposed in a conjugated position through the beam splitter and the area of the light receiving sensor being smaller than the area of the image sensor, wherein the modulated measurement light is a frequency modulated light and said central processing device is adapted to distinguish the reflection light image from said reflector from a light image other than the reflection light image based on a frequency of an output of said light receiving sensor, wherein the frequency modulated measurement light is pulsed light, and wherein said light receiving portion is further provided with a synchronization detecting circuit adapted to synchronously detect the output of said light receiving sensor based on said frequency modulated pulsed light; wherein the synchronization detecting circuit is adapted to outputs a coincidence signal toward the central processing device when a modulation frequency and a frequency of the output from the light receiving sensor coincide, and the central processing device is adapted to judge that the light image on the optical axis is the light image of the reflector.