To accurately specify relative position relationship between a rotation position of an opening driving motor and a height position of a heald frame.

A load torque detection circuit 24 calculates load torque from electric current value fed from a driving circuit 21 to an opening driving motor 20. Rotation position information obtained from an rotary encoder 202 of the opening driving motor 20 is fed to a decision circuit 25 and the decision circuit 25 specifies a reference position of the opening driving motor 20 based on variation pattern of load torque obtained from the load torque obtained from the load torque detected by the load torque detection circuit 24. A memory circuit 26 stores the standard position specified by the decision circuit 25.