PURPOSE: To ensure the normal operation of an ordinary transmitter, by pressurizing the inside by injecting high pressure gas into the inside of a flying body when shooting the flying body provided with said transmitter under low pressure at a high altitude.

CONSTITUTION: When an induction flying body provided with a normal transmitter is loaded on an aircraft and the flying body is shot under a low pressure condition at a high altitude, arcking is generated at the transmitter and the inside of a waveguide of a solid circuit if the pressure of the transmitter and the inside of the solid circuit is low pressure similar to pressure at the high altitude at the outside, thus frequently resulting in the dangers that the transmitter normally does not work. When shooting the flying body at low pressure, a heater 2 in a valve key device 1 is heated to ignite gunpowder 3, a plunger 4 is left moved by explosive power at that time to break an outlet cover 6 of a high pressure gas vessel 5, and high pressure gas is jetted into a transmission system 8 through a course 7 to increase internal pressure, thus eliminating said troubles.