To provide the electric cutter of lightweight shape steel which can cut off lightweight shape steel such as a joist along an opening edge by one operation and further cut even the lightweight shape steel projected to a circular opening finely along the open edge.

A cutter main body A constituted by erecting pillars 1b on both sides of a board shape base 1a, forming a fantail groove by a wedge shape groove 11 facing each other on the front edge of the faced surfaces of both pillars 1b and installing a plate shape edge 2 whose side is inserted in both grooves 11 and also sticking a screw shaft 4 penetrating the base part 1a to a receiving tool 3 installed on the lower part of the cutting edge, and a press cap 7 providing vertical grooves 74 on the lower surface position coping with the erected side plate of the light shaped steel which is a material to be cut, providing the hole 73 for the cutting edge penetrating in a vertical direction and installed to the upper end of the columnar part 1b attachably/ detachably are provided so that the cutting edge 2 is vertically moved while sliding in the groove 11 by the turning of the screw shaft 4.