1. A robot control apparatus controlling a robot body including an arm unit having a plurality of link members coupled with one another and a hand unit which is disposed at an end of the arm unit, which grasps a first workpiece, and which attaches the grasped first workpiece to a second workpiece, the robot control apparatus, comprising: a camera configured to output image data obtained by capturing an image of the robot body, the first workpiece, and the second workpiece; a first coordinate system calculation unit configured to calculate a first coordinate system representing a position and orientation of the hand unit in a camera coordinate system of the camera from the image data; a second coordinate system calculation unit configured to calculate a second coordinate system representing a position and orientation of the first workpiece in the camera coordinate system of the camera from the image data; a third coordinate system calculation unit configured to calculate a third coordinate system representing a position and orientation of the second workpiece in the camera coordinate system of the camera from the image data; a first coordinate transformation matrix calculation unit configured to calculate a first coordinate transformation matrix used to transfer the second coordinate system into the first coordinate system; a second coordinate transformation matrix calculation unit configured to calculate a second coordinate transformation matrix used to transfer the third coordinate system into the first coordinate system; a target-point setting unit configured to set, in a coordinate system of the first workpiece, coordinate data of a target point having a constant position and orientation relative to the first workpiece; an instruction-point setting unit configured to set, in a coordinate system of the second workpiece, coordinate data of an instruction point which allows the target point to pass in a constant position and orientation relative to the second workpiece; a first coordinate transformation unit configured to perform coordinate transformation on the coordinate data of the target point set by the target-point setting unit using the first coordinate transformation matrix; a second coordinate transformation unit configured to perform coordinate transformation on the coordinate data of the instruction point set by the instruction-point setting unit using the second coordinate transformation matrix; an operation instruction generation unit configured to generate operation instructions for operating the robot body so that the robot body traces a trajectory obtained such that the coordinate data of the target point which has been subjected to the coordinate transformation by the first coordinate transformation unit passes a position of the coordinate data of the instruction point which has been subjected to the coordinate transformation by the second coordinate transformation unit; and an operation instruction output unit configured to output the operation instructions generated by the operation instruction generation unit to the robot body.