A portable circular saw has a housing and a baseplate. The housing carries a motor which is connected to a blade through a transmission mechanism. The baseplate includes a main baseplate and a secondary baseplate each of which has a bottom surface and the bottom surfaces are coplanar. At least a part of the blade passes though a slot formed in the main baseplate. The main baseplate includes a first edge and a second edge disposed on opposing sides of the blade. The secondary baseplate has at least two exchangeable positions. In a first position, the secondary baseplate is jointed or adjacent to the first edge of the main baseplate and, in a second position, the secondary baseplate is joined or adjacent to the second edge of the main baseplate.