the present invention relates to an alloy type thermal fuse and a fuse element which are particularly useful as a thermoprotector for a battery . it is an object of the invention to provide an alloy type thermal fuse in which a ternary in — sn — bi alloy or an alloy in which ag or cu is added to the ternary alloy is used as a fuse element , or the fuse element wherein dispersion of the operating temperature can be satisfactorily suppressed , the operating temperature can be set to about 100 ° c . or lower , and the specific resistance and the mechanical strength of the fuse element can be sufficiently ensured . a low - melting fusible alloy serving as the fuse element has an alloy composition of 50 to 55 % in , 25 to 40 % sn , and balance bi . in a preferable range of the composition , in is 51 to 53 %, sn is 32 to 36 %, and a balance is bi .