PURPOSE: To measure a distance to an object by one television camera, by varying the horizontal direction of the television camera by a microscopic angle, and deriving a distance to an object to be photographed, from a moving extent of a target point on the monitor picture.

CONSTITUTION: A target point A reflected on a monitor picture 10 moves to a point B when a television camera is turned by a microscopic angle ΔQ in the horizontal direction, and a moving extent Xm is shown by the expression. (f), (a) and M denote a focal distance, a distance to an object to be photographed, and magnification to a monitor from a camera, respectively. A composite video signal 201 sent from a monitor television 21 is converted to a vertical synchronizing signal 203 and a horizontal synchronizing signal 204 by a synchronizing separating circuit 22 and a waveform shaping circuit 23, the target point on the monitor television 21 is inputted as a luminance signal to a light pen controller 24 through a light pen 25, the position is operated by its comparison and callation, Xm is derived, and a distance (a) to the object to be photographed is derived.