A radiofrequency electric current ablation catheter comprising a tip electrode, a means for detecting temperature of the tip electrode, a catheter shaft and a portion for operation at proximal end, wherein the tip electrode has a shape formed by connecting three or more spherical or approximately spherical surfaces having centers on the same straight line to each other with a curved surface. The catheter has the tip electrode which has a small diameter, is brought into excellent contact with organisms, can provide a great output power and is easily cooled with the circulating blood stream.
