A double safety device for a quick coupler, the device comprising: a quick coupler body 100 connectable to an arm of an excavator; a fixed hook 110 being provided on one side of the quick coupler body 100 and being coupled with a first attachment pin; a hitch 120 being provided on other side of the quick coupler body 100, being connected to a cylinder load 220 of a cylinder 200 and being coupled with a second attachment pin during forward motion of the cylinder load 220; and a locking means 300 for preventing an arbitrary release of coupled state of the fixed hook 110 and the first attachment pin; characterised in that the locking means 300 comprises: a fastening block 310 being positioned outside a cylinder tube 210 of the cylinder 200 and being fixed on the quick coupler body 100 a first compression spring 320 being provided on between the fasting block 310 and the hitch 120 and assigning an elastic compression force, a second compression spring 330 having an elastic compression force to push the cylinder tube 210 toward a body stanchion 150 and having one end supported on other side of the fastening block 310 and other end supported on the cylinder tube 210, a blocking block 340 being coupled with one side of the cylinder tube 210, being interlocked when the cylinder tube 210 moves and being positioned on upper side of the fastening block 110 to block a detachment of the fixed hook 110 and the first attachment pin 21 and a stopper member 380 being formed to protrude at one side or the other side of the fastening block 310, and limiting a backward motion of the hitch 120 or the blocking block 340 by contacting during the backward motion of the hitch 120 or the blocking block 340. a quick coupler body 100 connectable to an arm of an excavator; a fixed hook 110 being provided on one side of the quick coupler body 100 and being coupled with a first attachment pin; a hitch 120 being provided on other side of the quick coupler body 100, being connected to a cylinder load 220 of a cylinder 200 and being coupled with a second attachment pin during forward motion of the cylinder load 220; and a locking means 300 for preventing an arbitrary release of coupled state of the fixed hook 110 and the first attachment pin; characterised in that the locking means 300 comprises: a fastening block 310 being positioned outside a cylinder tube 210 of the cylinder 200 and being fixed on the quick coupler body 100 a first compression spring 320 being provided on between the fasting block 310 and the hitch 120 and assigning an elastic compression force, a second compression spring 330 having an elastic compression force to push the cylinder tube 210 toward a body stanchion 150 and having one end supported on other side of the fastening block 310 and other end supported on the cylinder tube 210, a blocking block 340 being coupled with one side of the cylinder tube 210, being interlocked when the cylinder tube 210 moves and being positioned on upper side of the fastening block 110 to block a detachment of the fixed hook 110 and the first attachment pin 21 and a stopper member 380 being formed to protrude at one side or the other side of the fastening block 310, and limiting a backward motion of the hitch 120 or the blocking block 340 by contacting during the backward motion of the hitch 120 or the blocking block 340.