To simplify and miniaturize the structure of a sealing device for a package that securely bonds together the layers of opposite plastic sheets, which are to be sealed, and to improve productivity.

The sealing device 20 for the package 10 includes a linear, planar sealing device 30 that uses a seal bar 31 having a linear sealing part 31A and a planar sealing part 31B. Using the linear sealing part 31A of the seal bar 31, the linear, planar sealing device 30 presses the layer 11A and 12A of the plastic sheets 11 and 12, which are to be sealed, under heat. Also, using the planar sealing part 31B of the seal bar 31, the device 30 presses the layers 11A and 12A of the plastic sheets 11 and 12 including the portions pressed by the linear sealing part 31A of the seal bar 31. Thus, the device 30 bonds together the layers 11A and 12A in a fused state.