Numerical controller of machine tool

A numerical controller of a machine tool which controls movement of a movable unit of a machine tool, the numerical controller comprising:

• a shape data storage unit which stores movable unit shape data which indicate a position and a shape of the movable unit and interfering structure shape data which indicate a position and a shape of an interfering structure with respect to the movable unit;
• a retracting direction determining unit which determines, on the basis of a current position and a movement control direction of the movable unit, a retracting direction of the movable unit for power outage;
• an interference determining unit which determines, on the basis of the movable unit shape data and the interfering structure shape data, presence or absence of interference between the movable unit and the interfering structure when the movable unit is moved in the retracting direction for power outage as determined by the retracting direction determining unit;
• a retracting position calculating unit which determines, on the basis of a determination result of the interference determining unit, an amount of retracting of the movable unit in the retracting direction for power outage which is determined by the retracting direction determining unit, and calculates a retracting position for power outage, on the basis of the retracting direction for power outage and the amount of retracting;
• and
• a power outage detecting unit which detects that supply of power to the numerical controller of machine tool is stopped, wherein
• when the power outage detecting unit detects stoppage of the supply of power, the movable unit is retracted to the retracting position for power outage.