A machine tool having a monolithic base is disclosed. The monolithic base includes at least two flat surfaces that are mutually orthogonal and that are convex with respect to each other. The machine tool includes at least two moveable stages, each mounted to one of the flat surfaces, and each stage also being mutually orthogonal.

An adjusting device for lifting and lowering a workbench is provided between a workbench and a workbench rest. An adjusting seat is firmly secured with the workbench rest and an adjusting wheel is screwed and locked on the adjusting seat. A screwing fastener is inserted through the underside of the workbench and the adjusting wheel, and an elastic member is provided between an upper flange of the screwing fastener and the topside of a fixed plate of the workbench. Thus, by the prestress of the elastic member pushing against the workbench, the workbench can be surely driven by screw rotation of the adjusting wheel and hence the adjusting wheel can easily drive the workbench to move up and down.