PURPOSE: To facilitate handling by providing a pointed projection movable to a bored position on a cover of a minicylinder sealed by a sealing plate easy to bore.

CONSTITUTION: A minicylinder 10 is sealed by a sealing plate 11 easy to bore and a pointed projection 30 is provided movably from non-boring position to boring position inside a cover 20. Thus, the pointed projection 30 is shifted by hitting or pressing the cover 20 to break through said sealing plate 11 and jet gas in the minicylinder 10, so that the handling of said minicylinder is facilitated without any special tools.