PURPOSE: To prevent application of a resilency energy accumulated at a flange tightening band on a rocket as an impact force when the rocket is separated by changing a distance from an axial line of the rocket to an engagement member, and providing an expansion member to get the engagement member from a flange at the band.

CONSTITUTION: For connecting rocket structural bodies 10, 11, flanges 12, 13 formed at the rocket structural bodies 10, 11 are engaged with an engagement groove 24 of an engagement member 22 of a flange tightening band 20, and both end parts 21b of an arc-like member 21 are connected with each other through a fixing member 21c. Prior to separating the rocket structural bodies 10, 11, the connection length of the arc-like member 21 is elongated to increase a distance R(radius) from an axial line P of the rocket structural bodies 10, 11 to the engagement member 22 to get the engagement member 22 apart from the flanges 12, 13, and firing bolts 21c, 21c are exploded in this condition to separate the arc-like members 21, 21 of the band 20 from each other.