A highly durable and compact chain disconnecting and connecting tool that may be used for a chain at a sprocket part for winding the chain and that can receive an operational load at two places is provided. A first block has an engaged pressure actuating member coupling member. A second block is coupled with the first block turnably by the coupling member and has a cutout on one side and a through hole on another side of the block. The tool is attached to the chain from an opening while positioned engagement with an edge projection of a tap bolt that is screwed with the first block and with the cutout or the through hole.