To avoid tracking of an interceptor missile under tracking by providing a collapsible/developable reflector on the side of a seaker for guided projectile and reflecting a radio wave outputted from a radio wave source such that a required reflection strength can be attained.

A collapsed reflector 16 is developed when a wire is wound around a motor 15 and reflects radio wave 8 from a radio wave source 7 thus increasing the intensity of radio wave being reflected from a projectile 1 when viewed from the front side. Receiving gain of an opponent tracking radar and an interceptor missile is varied in correspondence with increased current strength. Subsequently, a control circuit 14 reverse the motor 15 to rewind the wire thus collapsing the reflector 16. Strength of radio wave being reflected on the projectile 1 decreases and the receiving circuit in an opponent tracking radar and an interceptor missile misses the projectile 1 temporarily. Consequently, the projectile 1 can avoid attack from the interceptor missile.