1. A motion path search device comprising: a first space identification unit, via a computer system, configured to identify, as first spaces, three-dimensional spaces passed through by a movable part of a robot in a plurality of direct teaching operations performed by an operator to teach a motion to the robot, the direct teaching operations being performed by directly moving the robot using a hand of the operator; a second space identification unit, via the computer system, configured to identify, as second spaces, three-dimensional spaces occupied by at least a portion of a body of the operator during the direct teaching operations using a three-dimensional position measuring device mounted on the portion of a body of the operator; a spatial difference calculation unit configured to calculate a first differential space and a second differential space, the first differential space being a part of one of the first spaces which is identified as a result of one of the direct teaching operations and having no overlap with another of the first spaces which is identified as a result of another the direct teaching operations that precedes the one of the direct teaching operations, and the second differential space being a part of one of the second spaces which is identified as a result of the one of the direct teaching operations and having no overlap with another of the second spaces which is identified as a result of the other of the direct teaching operations that precedes the one of the direct teaching operations; a feedback unit configured to provide the operator with at least one of information regarding the first differential space and information regarding the second differential space; a space combining unit, via the computer system, configured to combine a first accessible space and a second accessible space, the first accessible space being a combination of the first spaces identified as results of the direct teaching operations, and the second accessible space being a combination of the second spaces identified as results of the direct teaching operations; and a path search unit, via the computer system, configured to search for a motion path of the movable part within a space resulting from the combining by the space combining unit, after the direct teaching operations are completed.