Patent ID: 7222702

Claim:
In a gas filling method for filling compressed gas into a gas spring comprising a cylinder main body; a rod member slidably inserted into said cylinder main body; a gas filled chamber inside of said cylinder main body and filled with compressed gas and applying a gas pressure on said rod member so as to urge said rod member in a first direction; a rod inserting hole for inserting said rod member which is formed on an end wall of said cylinder main body in a second direction opposite to said first direction; an annular collar slidably fitted around said rod member at a position apart from said rod inserting hole in said second direction; an annular groove formed on said annular collar and being open toward said second direction; and a lock ring engaging with an annular ring mounting groove formed on said rod member: said gas filling method is characterized by comprising steps of: filling said compressed gas into said gas filled chamber with the use of a gas filling jig; moving said rod member toward said second direction so as to allow said lock ring to engage with said ring mounting groove after filling of said compressed gas; moving said rod member in said first direction by said compressed gas in said chamber in a state in which said lock ring engages with said ring mounting groove, so as to introduce said lock ring into said annular groove formed on said annular collar; and locking said annular collar on an end wall of said cylinder main body.