PURPOSE:To accelerate a projectile much more and miniaturize an engine by a method wherein a branch electrode is provided at the side of the muzzle of one rail between a pair of accelerating rails provided in a launching unit to permit the igniting of a ramjet engine through the branch electrode upon accelerating the ramjet projectile electromagnetically. CONSTITUTION:When a ramjet projectile 10 is loaded into a launching passage 3 and, thereafter, a switch 6 is put ON, electric current is conducted through an annular solid armature 15 whereby the ramjet projectile 10 is accelerated electromagnetically. In this case, a through-hole 20 is formed in the projectile 10 from a suction hole 14 to an injection hole 13 and, therefore, the flow speed of air flowing through the through-hole 20, becomes about Mach 7-8 substantially the same as the speed of the projectile. Thereafter, when the projectile 10 is contacted with an initiating electrode 16 through the branch electrode 7 when the projectile 10 leaves the muzzle 3a of the rail gun 4, the excessive energy of a power supply 5 is thrown into a conductive phase 17 to explode it whereby solid fuel 12 is ignited. Then, a ramjet engine, operated by the solid fuel 12, is started and the projectile 10 is accelerated additionally.