An inductively coupled plasma generator having a lower aspect ratio reaction gas, comprising a chamber having a gas inlet through which a reaction gas is supplied, a vacuum pump for maintaining the inside of the chamber vacuum and a gas outlet for exhausting the reaction gas after completion of the reaction, a chuck for mounting a target material to be processed inside the chamber, and an antenna to which high-frequency power is applied, the antenna provided at the upper and lateral portions of the chamber, wherein the antenna has parallel antenna elements in which a discharge of a high frequency can be allowed and impedance is low to ensure a low electron temperature, the antenna is disposed such that a powered end of each of the antenna elements and a ground end of each of the antenna elements opposite to the powered end are symmetrical in view of the center of an imaginary circle formed by the antenna to establish rotation symmetry of plasma density profiles, the antenna elements are twisted in a helical manner, and the powered end of each of the antenna elements is positioned to be far from the chamber and the ground end of each of the antenna elements is positioned to be close to the chamber, thereby compensating for a drop in the plasma density due to ion loss occurring at the powered end.