A control apparatus of a machine tool, the control apparatus including: a numerical control unit configured to create a spindle axis command and a feed axis command according to a tapping program; a spindle axis control unit configured to control rotational operation of the spindle axis according to the spindle axis command; a rotation detector configured to detect a rotation position of the spindle axis; and a feed axis control unit configured to control feeding operation of the feed axis according to the feed axis command on the basis of the rotation position. The numerical control unit is further configured to include, in the spindle axis command, a speed command value during return that does not depend on maximum rotation speed during machining of the spindle axis and that is higher than the maximum rotation speed during machining, as a command of return operation.