To provide an automatic focusing device for a liquid crystal projector which can automate a projection lens focusing means.

The automatic focusing device is constituted of a projection lens 1 having a focusing means, a focusing mechanism 2 for focusing the lens 1, a semitransparent reflection film means 3 arranged between a dichroic mirror or dichroic prism 4, a light receiving element 5 arranged on a position equivalent to an optical axis distance between the lens 1 and LCDs 14r, 14g, 14b so as to receive reflected light from a screen S through the means 3 and convert the received signal into a received light output signal, a focusing control part 6 for detecting and calculating a focus position up to the screen S by the received light output signal from the element 5 and controlling the drive of the mechanism 2, and a position detector 7 for detecting a position focused by the mechanism 2.