A quick coupler located at a front end of an arm of a boom pole disposed in heavy equipment to attach or detach an attachment, characterized by the quick coupler comprising: a coupler body connected to the front end of the arm of the heavy equipment; a fixed hook formed in the coupler body and to which a first coupling pin of the attachment is fitted; a mobile hook rotatably coupled to the coupler body and to which a second coupling pin of the attachment is fitted; a hydraulic cylinder having a slot formed in any one of a cylinder rod and a cylinder body and fitted to a cylinder shaft of the coupler body and the other one rotatably coupled to the mobile hook , including a cylinder hook formed near the slot , and configured to rotate the mobile hook to be coupled to or released from the second coupling pin according to an extension or contraction operation; a rotary key rotatably coupled to the coupler body , including a rotary key protrusion that is inserted into or withdrawn from a coupling groove of the fixed hook according to a rotary position, wherein the rotary key protrusion is maintained in a state of being inserted into the coupling groove of the fixed hook by an elastic force of a rotary key spring and prevents detachment of the first coupling pin from the coupling groove of the fixed hook ; and a stopper including a stopper hook coupled to or separated from the cylinder hook , supported by an elastic force of a stopper spring , and configured to rotate the rotary key so that the rotary key protrusion is withdrawn from the coupling groove of the fixed hook during a contraction operation of the hydraulic cylinder in a state in which the stopper hook is coupled to the cylinder hook . a coupler body connected to the front end of the arm of the heavy equipment; a fixed hook formed in the coupler body and to which a first coupling pin of the attachment is fitted; a mobile hook rotatably coupled to the coupler body and to which a second coupling pin of the attachment is fitted; a hydraulic cylinder having a slot formed in any one of a cylinder rod and a cylinder body and fitted to a cylinder shaft of the coupler body and the other one rotatably coupled to the mobile hook , including a cylinder hook formed near the slot , and configured to rotate the mobile hook to be coupled to or released from the second coupling pin according to an extension or contraction operation; a rotary key rotatably coupled to the coupler body , including a rotary key protrusion that is inserted into or withdrawn from a coupling groove of the fixed hook according to a rotary position, wherein the rotary key protrusion is maintained in a state of being inserted into the coupling groove of the fixed hook by an elastic force of a rotary key spring and prevents detachment of the first coupling pin from the coupling groove of the fixed hook ; and a stopper including a stopper hook coupled to or separated from the cylinder hook , supported by an elastic force of a stopper spring , and configured to rotate the rotary key so that the rotary key protrusion is withdrawn from the coupling groove of the fixed hook during a contraction operation of the hydraulic cylinder in a state in which the stopper hook is coupled to the cylinder hook . <EOS>