PURPOSE: To provide a bag with two lateral seals: a gusset seal on one end thereof and a pillow seal on the other, by separating a completely bagged portion provided with a top seal and the subsequent cut from a packing cylinder and effecting a bottom seal for use as the subsequent bag after placing a gusset on the lower part of said packing cylinder.

CONSTITUTION: A top seal 8 and a cut 11 are made by a lateral sealer 6 where a packing cylinder 5 moves down to a position lower than a cylinder 3 by a distance of a bag or a bag and half and the lower part of the subsequent bag is provided with a gusset 17 by moving two backing boards 12 and 13 down a cylinder 2b in a pair, parted right and left, and by means of gusset members 14 and 15 entering between these backing boards from the outside and with a lateral seal 9 made by a lateral sealer 7. Afterwards, when the lateral sealers 6 and 7, a cutter 10 and gusset members 14 and 15 in a closed condition are all released, a completely packed product S drops, with the bottom seal 9 being a gusset seal and the top seal a pillow seal.