A working device comprising: an attachment for work; an arm to which the attachment for work is vertically swingably attached at a first end of the arm ; a first link member pivotally joined, vertically swingably, at a first end to the arm ; a second link member pivotally joined, vertically swingably, at a first end to the attachment and at a second end to a second end of the first link member while the attachment is vertically swingably attached to the arm; and an attachment hydraulic actuator pivotally joined, vertically swingably, at its base end to the arm and to vertically swing the attachment with respect to the arm , wherein the working device comprises a connection unit connectable to the first link member and operated by the attachment hydraulic actuator , wherein the working device is configured such that the first link member can be vertically swung by the attachment hydraulic actuator via the connection unit connected to the first link member , wherein the working device is configured such that the first link member and the connection unit can be connected switching selectively between a plurality of positions, wherein the connection unit comprises a housing having openings open to right and left directions which are perpendicular to the vertical directions and a connection pin mechanism provided in the housing ; and wherein the connection pin mechanism comprises connection pins provided in the housing to be protruded and retracted through the openings in right and left directions and a connection pin operating actuator provided in the housing for protruding and retracting the connection pins in the housing , and wherein the working device comprises a connection switching means operated to work so as to switch the connection position of the first link member with the connection unit . an attachment for work; an arm to which the attachment for work is vertically swingably attached at a first end of the arm ; a first link member pivotally joined, vertically swingably, at a first end to the arm ; a second link member pivotally joined, vertically swingably, at a first end to the attachment and at a second end to a second end of the first link member while the attachment is vertically swingably attached to the arm; and an attachment hydraulic actuator pivotally joined, vertically swingably, at its base end to the arm and to vertically swing the attachment with respect to the arm , wherein the working device comprises a connection unit connectable to the first link member and operated by the attachment hydraulic actuator , wherein the working device is configured such that the first link member can be vertically swung by the attachment hydraulic actuator via the connection unit connected to the first link member , wherein the working device is configured such that the first link member and the connection unit can be connected switching selectively between a plurality of positions, wherein the connection unit comprises a housing having openings open to right and left directions which are perpendicular to the vertical directions and a connection pin mechanism provided in the housing ; and wherein the connection pin mechanism comprises connection pins provided in the housing to be protruded and retracted through the openings in right and left directions and a connection pin operating actuator provided in the housing for protruding and retracting the connection pins in the housing , and wherein the working device comprises a connection switching means operated to work so as to switch the connection position of the first link member with the connection unit . <EOS>