A system for bonding an electrode assembly to a separator, comprising: a secondary battery laminating device, an electrode assembly and a separator, wherein the secondary battery laminating device comprises a transfer part transferring the electrode assembly in a state in which the electrode assembly is disposed on the separator, and a bonding part disposed on a transfer path of the transfer part to contact an entire surface of the electrode assembly and apply heat to the electrode assembly, thereby bonding the electrode assembly to the separator, wherein the electrode assembly comprises an electrode and an electrode tab protruding from an end of the electrode, and the bonding part has a stepped portion to contact the electrode tab and the electrode, wherein the separator has a width that extends outward from an end of the electrode assembly, and the bonding part has a stepped portion to contact all the electrode assembly and the separator, wherein a surface of the bonding part, which faces the electrode assembly, is divided into three areas having stepped surfaces different from each other, which are a first area, a second area, and a third area, wherein the first area is an area that contacts the electrode tab when the bonding process is performed, and the second area is an area that contacts a surface of the uppermost electrode, which is exposed to the outside, and the third area is an area that directly contacts the separator disposed on an area on which the electrode is not disposed, and wherein the bonding part, when in use, presses the electrode assembly and applies heat to the electrode assembly so that the electrode assembly and the separator, which are stacked on each other, are bonded to each other. a secondary battery laminating device, an electrode assembly and a separator, wherein the secondary battery laminating device comprises a transfer part transferring the electrode assembly in a state in which the electrode assembly is disposed on the separator, and a bonding part disposed on a transfer path of the transfer part to contact an entire surface of the electrode assembly and apply heat to the electrode assembly, thereby bonding the electrode assembly to the separator, wherein the electrode assembly comprises an electrode and an electrode tab protruding from an end of the electrode, and the bonding part has a stepped portion to contact the electrode tab and the electrode, wherein the separator has a width that extends outward from an end of the electrode assembly, and the bonding part has a stepped portion to contact all the electrode assembly and the separator, wherein a surface of the bonding part, which faces the electrode assembly, is divided into three areas having stepped surfaces different from each other, which are a first area, a second area, and a third area, wherein the first area is an area that contacts the electrode tab when the bonding process is performed, and the second area is an area that contacts a surface of the uppermost electrode, which is exposed to the outside, and the third area is an area that directly contacts the separator disposed on an area on which the electrode is not disposed, and wherein the bonding part, when in use, presses the electrode assembly and applies heat to the electrode assembly so that the electrode assembly and the separator, which are stacked on each other, are bonded to each other.