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a rotary key rotatably coupled to the coupler body, including a rotary key protrusion that is inserted into or withdrawn from a coupling groove of the fixed hook according to a rotary position, wherein the rotary key protrusion is maintained in a state of being inserted into the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by an elastic force of a stopper spring, and configured to rotate the rotary key so that the rotary key protrusion is withdrawn from the coupling groove of the fixed hook during a contraction operation of the hydraulic cylinder in a state in which the stopper hook is coupled to the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.