[Object] It is intended to provide a new and improved apparatus which can successively make plastic bags each of which includes an end surface provided with a protrusion, without making a web of bottom gusset material supplied specially. [Solution] A first web of panel material 1 is folded along a first folded line 5 at a position adjacent to a side edge 21 of first web of panel material 1 while a second web of panel material 2 is folded along a second folded line 6 at a position adjacent to a corresponding side edge 22 of second web of panel material 2. A first folded portion 23 is formed in the first web of panel material 1. There exists a distance between the side edge 21 and the first folded line 5, which is larger than twice a distance between the corresponding side edge 22 and the second folded line 6 by a predetermined distance L3, after being folded. The end surface is formed by the first folded portion 3, the protrusion being formed by the predetermined distance L3.