PURPOSE: To locarize an existence region of a plasma armature and hence suppress a portion between rails being filled up with gas produced in the armature part by providing a through-hole in a shooter perpendicularly to a rail surface, and further providing a fuse.

CONSTITUTION: A through-hole 6 is provided in a shooter 2 disposed between two rails 1 perpendicularly to a rail surface, and a fuse 5 is disposed in the through-hole. Once voltage is applied from a power supply 4 to the rail 1, a large current flows through the fuse 5, whereby the fuse is vaporized into plasma by Joule heat. Hereby, no new arc plasma is generated between the rails outside the shooter, whereby elongation of the plasma armature and generation of two-dimentional arc plasma are suppressed. Further, the plasma 2 makes contact only with the rails and does not contact with the insulator 7 supporting the rails, so that fusion and evaporation of the insulator by the plasma can be prevented.