To provide a portable electric circular saw which can cut an object straight without using a criterion parallel in the cutting direction.

The portable electric circular saw X is provided with a surface plate 20 fixed to the electric circular saw, a movement member 30 fixed slidably in the cutting direction to the surface plate, and a contact member 40 comprising a board having a plane contacting the front edge of the object fixed to the front edge of the movement member. By moving the surface plate and an electric circular saw main body 10 along the movement member while the contact member is contacted with the front edge of the object, the object can be cut straight. Since the criterion is made the front edge of the object, if the object is rectangular in a plan view, straight cutting is possible. The criterion in the cutting direction, even if difficult to be used, can be used relatively easily.