1. A method of detecting a work start point in a robot of the teaching playback control type having an interpolating function in which a work tool is attached to an edge of an arm and a visual sensor is provided for the wrist portion of said arm and a contact sensor is provided for generating a contact signal when an edge of said work tool comes into contact with an object to be worked is further provided, whereby a plurality of drive shafts constituting the robot are controlled in response to position correcting signals from said visual sensor, thereby adjusting a position of said work tool, said method comprising the steps of: (1) using said visual sensor to image-recognize a work line of said work object and said work tool; (2) generating said position correcting signal, in a first correcting direction, for reducing a first distance between said work line and said edge of said work tool on the basis of said image recognized by said visual sensor; (3) moving said edge of said work tool along said first correcting direction in response to said position correcting signal until said work line and said edge of said work tool substantially coincide on said recognized image; and (4) moving said edge of said work tool along an axial direction of said work tool until said contact sensor generates a contact signal and, at the same time, correcting a position of said edge of said work tool along said first correcting direction until said work line and said edge of said work tool on said image substantially coincide.