A machine tool controller including a numerical control section, a spindle-axis control section and a feed-axis control section. The spindle-axis control section includes a section for making the spindle axis perform an accelerated rotation at maximum capacity from a process start position toward a target thread depth, with a maximum rotation speed set as a target value; a section for detecting a maximum acceleration during the accelerated rotation based on a rotational position; a section for detecting a residual rotation amount from a current position to the target thread depth, based on a total rotation amount and the rotational position; a section for detecting a current speed based on the rotational position; and a section for making the spindle axis perform a decelerated rotation at maximum capacity to reach the target thread depth after the accelerated rotation, based on the maximum acceleration, the residual rotation amount and the current speed.