To provide a lead-free alloy thermal fuse having excellent operational reliability in the range of 100 to 150°C, without including no lead and cadmium having environmental problem.

This thermal fuse is constituted by connecting a thermosensitive device and a terminal lead, covering them with a case of an insulating material and sealing an end part for deriving the terminal lead from the case of the insulating material. In the temperature fuse, the thermosensitive device is provided with a solid-liq. coexistent region, a non-eutectic alloy in which a difference of the liquidus line temperature and the solidus line temperature is less than 13°C is used, the alloy is joined to a plating part of the terminal lead partially plated with a plating material easy to be joined by the alloy, and the terminal lead itself is made of a metal in which the alloy is difficult to diffuse. The non-eutectic alloy has the alloy composition of a fusible alloy composed of In 50 wt.% to 53 wt.%, Bi 4.5 wt.% to 6.5 wt.%, Cu 0.1 wt.% to 1.0 wt.%, Ag 0.1 wt.% to 1.0 wt.% and remainder Sn. The non-eutectic alloy is joined to a Sn, Cu, Sn-Cu or Sn-Bi partial plated electrode part provided a Ni-based terminal lead.