The utility model relates to a mechanical automatic vertical drilling tool which comprises a conversion joint, a flow diversion head, a bearing, a balancing weight, a mandrel, an inner cylinder, an inner cylinder baffle plate, an upper disk valve, a lower disk valve, a shell body, a piston barrel baffle plate and a piston. The utility model has the principle that the utility model induces gravitational signals of well deviation in real time, and a gravitation driving mechanism is used for building a passage between high and low pressure fluid inside and outside a drilling column; the pressure difference between the high and the low pressure fluid is used for driving the piston to push a high edge of a well wall in real time, and the reaction force of the well wall pushes a drilling head to a lower edge, while at other positions of a well hole, the piston does not push the well wall and the drilling column rotates. The course circulates continuously, so that the well deviation state is induced and corrected continuously. The utility model can realize deviation prevention actively and in real time, effectively release drilling pressure, greatly enhance drilling rate and well hole quality and reduce construction risks. The utility model has the characteristics of simple and reliable structure, various drilling platforms, low cost of manufacture, use and maintenance, etc.