Reducing material for gas pressure welding and gas pressure welding method

A gas pressure welding method comprising the steps of:

• attaching a reducing material for gas pressure welding having a cap body with a height larger than a predetermined gap to one material to be pressure-welded, whose tip surface is disposed facing a tip surface of an other material to be pressure-welded with the predetermined gap therebetween, by fitting the reducing material for gas pressure welding from a side surface of the one material to be pressure-welded so that a top portion of the cap body comes in contact with the tip surface of the one material to be pressure-welded;
• and
• with the cap body attached, sandwiching the top portion between the tip surfaces of the one material to be pressure-welded and the other material to be pressure-welded and heating them, wherein
• the cap body has a body portion, formed with an opening/closing part, that can be fitted around the one material to be pressure-welded from the side surface so that the top portion of the cap body comes in contact with the tip surface of the one material to be pressure-welded,
• the body portion is constituted of a plurality of side plates, and each of the plurality of side plates attaches to the top portion of the cap body,
• one of the plurality of side plates can swing, and the opening/closing part of the body portion can be opened and closed by swinging of the one of the plurality of side plates, and
• the plurality of side plates other than the one of the plurality of side plates are integrated in a circumferential direction.