To provide an automatic tracking device for keeping fixed the traveling direction of the second harmonic light even in the case that the wavelength is changed like second harmonic laser generation using a wavelength tunable laser.

The automatic tracking device for keeping fixed the direction of the second harmonic of laser is provided with a prism which separates fundamental wave laser and the second harmonic laser and is placed and fixed on a turntable, a beam splitter which splits the separated fundamental light or second harmonic light, a position sensing detector which detects the position of split beams, and a controller which compares the traveling direction detected by the position sensing detector with a desired traveling direction and displaces the turntable, on which the prism is placed and fixed, in the peripheral direction so that the extent of variation may be zero.