To provide a controller for a machining device that controls oscillation of a cutting tool used for oscillating cutting to become capable of reducing a probability of interference between an interfering object existing near a work as a cutting target and the cutting tool. A controller for control over a machine tool comprises: a position command acquiring unit that acquires a position command directed to a servo motor for driving a cutting tool; a rotation speed acquiring unit that acquires a rotation speed of the cutting tool; an acceleration calculating unit that calculates an acceleration of the servo motor based on the position command; an oscillation command calculating unit that calculates an oscillation command based on the position command and the rotation speed, the calculated oscillation command causing the cutting tool and the work to oscillate relative to each other along a machining route; an offset value calculating unit that calculates an offset value based on the acceleration; an offset unit that offsets amplitude of the oscillation command; and a driving unit that outputs a drive signal to be used for driving the servo motor based on the oscillation command including the offset amplitude and the position command.