To provide a machine tool allowing an easy replacing work of a tool and improvement of workability.

In an NC lathe (machine tool) having a cover 3 disposed so as to surround the outside of a machine body 2 in the machine body 2 constituted by disposing a carriage 5 mounted with a tool rest 6 thereon on a side near a worker on a fixed bed 4 and disposing a headstock 7 mounted with a work W thereon on a side far from the worker on the fixed bed 4, a door opening 52 is formed and a side surface door 53 for opening/closing the door opening 52 is disposed at a part facing to the tool rest 6 on a side surface wall 3c of the cover 3 from the viewpoint of the worker side.