A machine tool has an oscillating axis that reciprocates in an optional region. A numerical controller that controls the machine tool designates positions of a lower dead point and a upper dead point when the oscillating axis of the machine tool reciprocates, and a reference speed during the oscillating operation when the oscillating axis reciprocates. The numerical controller then calculates, from the current position of the oscillating axis, a current phase in the case where one stroke of the oscillating axis is defined as one cycle, and calculates the speed of the oscillating axis at the current phase based upon the calculated current phase and the reference speed.