To facilitate jointing by forming a cap section provided in the upper section of a contractable joint material into a shape comprising a plurality of linear members orthogonally abutting on each other.

A linear joint body 2 is formed of plastic material such as polyurethane foam and polyethylene foam. The members of a cap section 3 with a U shaped cross section are made of plastic, butyl rubber, EPT rubber such as soft vinyl chloride or polyethylene. The members for cap 3 are arranged orthogonally crossed and are integrated into a body, forming the crossing cap 3. In addition, the upper section of the joint body 2 is fittedly installed in the U shaped recessed section, forming a contractable formed joint member 1. Through such operation, simply connecting the ends of the joint body 2 in a line is enough for executing jointing work, facilitating jointing work.