To solve the problem that use of a cutting tool such as scissors or a knife for opening of vacuum-packed food product or packaged merchandise product involves injury, while use of various long and short clips or the like for sealing is inconvenient due to their limitation to specific purposes/parts.

The easy fastener S is formed of a resilient conical spring 1 having a proper dimension and shape. An opening 7 of a bag B2 is narrowed and twisted, and the twisted part is inserted and locked from the large-diameter lower side of the conical spring 1 to the small-diameter upper side thereof, or inserted and locked in a transverse direction of the conical spring (between spiral pitches).