PURPOSE: To improve the accuracy and safety of cutting operation, while the linear cutting operation is easily achieved by arranging a circular saw and the guide protrusion of a rearward guide mechanism so that the circular saw cuts into the material to be worked and the guide protrusion is brought in contact with the cross section thereof.

CONSTITUTION: A forward guide mechanism A is provided in the forward part on the extending line of the blade 3 of a circular saw, and a rearward guide mechanism B is provided near the rearward part thereof. In the forward guide mechanism A, a long hole 7 having the direction perpendicular to cutting advancing direction is provided on an indicating piece 6. The indicating side 6' of the indicating piece 6 is screw-fitted into the screw hole provided at the forward part of the base 4 with a screw 4' so as to be fitted onto the side-extending line of the blade 3 of the circular saw. The rearward guide mechanism B screw-fixes a guide rod 8 rear the rearward part of the base 4 on the linear extending line connecting the indicating side 6' and the side of the circular saw 3. The lower end of the guide rod 8 is projected from the lower surface of the base 4 and becomes the guide protrusion 8' in contact with one or both of the cross sections W, W' of the material to be worked cut by the blade 3 of the circular saw.