To provide a main spindle moving type lathe capable of machining with and without a guide bush, and capable of easily performing the switching work.

A guide bush holder 13 provided with a guide bush 17 is removably fitted to a supporting base 12 before a headstock 2 holding a main spindle 3 so that a work W can be machined in a condition where the work is guided by the guide bush 17. The bush holder 13 is detached, a cover member 14 is fitted in place thereof, and a chuck nut 9c of a tip of the main spindle is inserted in a protection hole 18 formed in the cover member 14 to enable the machining without the guide bush.