To provide a seal gun capable of ejecting a paste-type sealing agent contained in a cylindrical container with a relatively wide diameter by pressurized air.

An adapter 12 has a large diameter part and a small diameter part on both sides which can be freely joined to a cylindrical container 13 and a grip 11, respectively by screwing. The cylindrical container 13 comprises a piston freely slidable in the inside and holds a pasty sealing agent in the inside space in the tip end side in relation to the piston. Pressurized air is introduced into the inside of the cylindrical container 13 through the adapter 12 when a slide switching part 25 of the grip 11 is switched to the opening position to push the piston in the inside of the cylindrical container 13 toward the tip end side of the cylindrical container 13, and thus the pasty sealing agent in the inside of the cylindrical container 13 is ejected from a conical nozzle 14.