Time information t and positional information about each axis are obtained, and the three-dimensional coordinates of tool center point Pe at time t are calculated to display the path of the tool center point Pe at time t. Then, whether a fixed time has elapsed or not is decided. If the fixed time has elapsed, the coordinates of the tool vector start point Ps at time t are calculated to display a line segment connecting between tool vector start point Ps and tool center point Pe, which is the end point of the tool vector. This display enables the orientation of the tool at each tool center point to be grasped at a glance.