Provided is a fine wire sheath heater with improved reliability. A sheath heater according to one embodiment of this invention comprises: a metal sheath; a heating wire positioned inside the metal sheath with a gap therebetween, the heating wire having a ribbon shape and being positioned so as to rotated about the axial direction of the metal sheath; an insulating material positioned in the aforementioned gap; and connecting terminals which are positioned on one end of the metal sheath, each connecting terminal being electrically connected to one end of the heating wire.