An off-line teaching device, for adjusting a vision sensor and carrying out set-up work off-line, which used to be done in the field, so as to reduce the operation time in the field. The off-line teaching device has a storing device for storing data including the shapes and the dimensions of a workpiece, a robot and a vision sensor, and a display for indicating images of the workpiece, the robot and the vision sensor. The teaching device also has a simulation program for generating the images of the workpiece, the robot and the vision sensor on the display and for calculating measurement data of the vision sensor based on the arrangement of the images on the display, and a sensor program for carrying out measurement on the display by the vision sensor based on the measurement data.