PURPOSE: To improve reliability in a screw clamping process, by installing a device, which accurately detects such one that is hard to discriminate the hole position, in a screw clamping machine with an automatic positioning device to be used in the screw clamping process in a production line.

CONSTITUTION: A screw clamping device consists of an X-Y table 2, a screw clamping head 3 clamping a screwed body 6 attached to this table 2, a camera 4 being attached to the screw clamping head 3 at a specified interval and detecting a hole position, a control unit 1 controlling both motions in the X-Y table and the screw clamping head 3 and a hole position detecting control device 5 which calculates the hole position and hole slippage taken by the camera 4. In the case where another hole exists in and around a hole of the screwed body 6, a mark 9 of a fitting-up hole or the like is caught with the camera 4, making it calculate the slippage of the mark 9 and the hole position of the screwed body 6, then this slippage is transmitted to the control unit 1, and a position of the X-Y table 2 is compensated, thus screw clamping motion takes place.