The microwave tissue coagulation instrument comprises: a shielded wire (10) in which an outer conductor (16) is disposed around an inner conductor (12) with a dielectric layer (14) therebetween and a helical antenna (2), which is connected to the inner conductor (12) of said shielded wire (10). The helical antenna (20) comprises: a tip end antenna (24) for radiating microwaves forward at the front from the tip of the shielded wire (10) and a base end antenna (26), which is connected to the tip end antenna (24), is wound around the shielded wire (10), extends toward the base end of the shielded wire (10), and radiates microwaves to the sides of the shielded wire (10). Electricity is supplied to the helical antenna (20) via the shielded wire (10) and the surrounding tissue is heated and coagulated by the microwaves irradiated from the helical antenna (20).
