PURPOSE: To apply to a small-sized pole plate as well, by punching out a strap from a metal plate, pressurizing metal plate portions located on the extensions of the slits in the lengthwise direction thereof, and bending the metal plate portions each falling within the width corresponding to the slit width.

CONSTITUTION: A strap 1 is punched out from a metal plate, metal plate portions on the extensions of the slits in the lengthwise direction thereof are pressurized, and the metal plate portions 3 falling within the width corresponding to the slit 2 width are upwardly or downwardly projected in the form of 'V'. Thus, a strap 1' having slits 2' whose width is made smaller, by a specified dimension, than the original width of each slit 2 is obtained. It is noted that in case the bent portion 4 is formed in such a manner as to be downwardly directed, adjustment is made of the degree of bending so that the bent portion 4 may not become an obstacle to operation of welding an electrode pole and installing it on the upper surface. Thus, it is possible to suitably adjust to a desired slit 2' width. Thus, a strap 1 having a width smaller than the plate thickness is obtained.