PURPOSE: To perform the positioning of a member to be cut, which is to be supplied to a shearing machine, automatically.

CONSTITUTION: A positioning device is provided with positioning members 21, 22, which are respectively provided in the cutting blade 2 side of a member W to be cut (X direction), which is to be supplied, and in the vertical direction (Y direction), a support member 3 for supporting the center of rotation of the member W to be cut, a driving mechanism 8 for making the support member 3 go forward and backward in the X direction, and a control mechanism 23 for controlling them. Each positioning member 21, 22 is provided with projections 25, 42, which abuts on the member to be cut, and the control mechanism 23 computes the position of each positioning member 21, 22 and the support member 3 on the basis of the dimension of the member to be cut and the dimension of a cutting circle, and moves each projection 25, 42 and the support member 3 to a computed predetermined position. A member to be cut can be thereby positioned by only inputting the dimension of the member to be cut and the dimension of the cutting circle into a control mechanism.