The rectangular planar-type ICP (Inductively Coupled Plasma) antenna having a balanced ratio of a magnetic field and an electric potential is capable of improving uniformity of plasma as well as improving a density of plasma. The planar-type ICP antenna includes first and second antenna elements spirally shaped outwards from an end thereof, respectively. The ends of the fist and second antenna elements are interconnected by means of a grounded common terminal. A RF power source is connected to a powered common terminal for connecting first and second powered terminals that are the other ends of the first and second antenna elements. The first and second powered terminals are arranged in peripheral portions of the antenna and the grounded common terminal is arranged in a center portion of the antenna in order to compensate for a drop of plasma ion flux in a region to which power is applied.