A work attachment attachable to a base machine of an operating machine, comprising: a boom to be attached to the base machine to be able to be raised and lowered; an inter-boom attached to a leading end of the boom rotatably about a horizontal axis; an arm with a base end part attached to a leading end of the inter-boom rotatably about a horizontal axis; a working device attached to a leading end part of the arm rotatably about a first shaft (J3); a boom cylinder for raising and lowering the boom ; an inter-boom cylinder provided between the boom and the inter-boom for rotating the inter-boom ; an arm cylinder provided between the inter-boom and the arm for rotating the arm ; a working device cylinder including one end attached to the arm for rotating the working device ; and a link mechanism connected to the other end of the working device cylinder rotatably about a third shaft (J5), wherein the working device is connected to the link mechanism so as to be rotatably about a second shaft (J4); wherein: the boom , the inter-boom and the arm are folded in three by contracting the inter-boom cylinder and the arm cylinder most and by folding into a state where the boom is located at an upper side of the inter-boom and the arm is located at a lower side of the inter-boom by laying down the boom to ground the arm ; and the working device cylinder and the link mechanism are provided at an upper surface side of the leading end part of the arm in the folded state, wherein the second shaft (J4) is located above the first shaft (J3) in the folded state, and the inter-boom cylinder and the arm cylinder are provided at an upper surface side of a base end part of the arm in the folded state so that a grounding part groundable over a length range sufficient to support the entire work attachment in the folded state is formed on the arm . a boom to be attached to the base machine to be able to be raised and lowered; an inter-boom attached to a leading end of the boom rotatably about a horizontal axis; an arm with a base end part attached to a leading end of the inter-boom rotatably about a horizontal axis; a working device attached to a leading end part of the arm rotatably about a first shaft (J3); a boom cylinder for raising and lowering the boom ; an inter-boom cylinder provided between the boom and the inter-boom for rotating the inter-boom ; an arm cylinder provided between the inter-boom and the arm for rotating the arm ; a working device cylinder including one end attached to the arm for rotating the working device ; and a link mechanism connected to the other end of the working device cylinder rotatably about a third shaft (J5), wherein the working device is connected to the link mechanism so as to be rotatably about a second shaft (J4); wherein: the boom , the inter-boom and the arm are folded in three by contracting the inter-boom cylinder and the arm cylinder most and by folding into a state where the boom is located at an upper side of the inter-boom and the arm is located at a lower side of the inter-boom by laying down the boom to ground the arm ; and the working device cylinder and the link mechanism are provided at an upper surface side of the leading end part of the arm in the folded state, wherein the second shaft (J4) is located above the first shaft (J3) in the folded state, and the inter-boom cylinder and the arm cylinder are provided at an upper surface side of a base end part of the arm in the folded state so that a grounding part groundable over a length range sufficient to support the entire work attachment in the folded state is formed on the arm . <EOS>