A heat-reactive switch comprising: an airtight container formed by adhering a lid plate in an airtight manner to an open end of a metallic, long, dome-shaped housing; two conductive terminal pins (4A, 4B) respectively inserted into two through holes provided in the lid plate, and each fixed in an airtight manner by an electrical insulating filler; a fixed contact fixed to one of the conductive terminal pins inside the airtight container; a heater having one end connected to the other of the conductive terminal pins and the other end connected to the lid plate inside the airtight container; a heat-reactive plate having one end connected to an inner surface of the housing, and whose curving direction is reversed at a predetermined temperature; and a movable contact provided on the other end of the heat-reactive plate, and constituting a pair of switching contacts with the fixed contact, wherein: a heating element of the heater has a plurality of meandering portions (7C, 7D) formed of a strip-shaped metal plate, and is arranged parallel to and between the lid plate and the heat-reactive plate; and the meandering portions (7C, 7D) are arranged such that two of the meandering portions are opposite to each other with the conductive terminal pin interposed therebetween, each aligned with an inner circumferential surface of the housing, and are each bent with respect to a reference axis extending in the longitudinal direction of the housing, so that strip-shaped flat portions face each other, wherein each of the two meandering portions (7C, 7D) is formed by alternately connecting a plurality of heater units including a linear portion and a semicircular portion, characterized in that each of the two meandering portions (7C, 7D) is bent such that a first surface of both surfaces of the linear portion faces the same first surface, and each of the two meandering portions (7C,7D) is bent 180 degrees twice with respect to two reference axes extending in the longitudinal direction of the housing. an airtight container formed by adhering a lid plate in an airtight manner to an open end of a metallic, long, dome-shaped housing; two conductive terminal pins (4A, 4B) respectively inserted into two through holes provided in the lid plate, and each fixed in an airtight manner by an electrical insulating filler; a fixed contact fixed to one of the conductive terminal pins inside the airtight container; a heater having one end connected to the other of the conductive terminal pins and the other end connected to the lid plate inside the airtight container; a heat-reactive plate having one end connected to an inner surface of the housing, and whose curving direction is reversed at a predetermined temperature; and a movable contact provided on the other end of the heat-reactive plate, and constituting a pair of switching contacts with the fixed contact, wherein: a heating element of the heater has a plurality of meandering portions (7C, 7D) formed of a strip-shaped metal plate, and is arranged parallel to and between the lid plate and the heat-reactive plate; and the meandering portions (7C, 7D) are a heating element of the heater has a plurality of meandering portions (7C, 7D) formed of a strip-shaped metal plate, and is arranged parallel to and between the lid plate and the heat-reactive plate; and the meandering portions (7C, 7D) are arranged such that two of the meandering portions are opposite to each other with the conductive terminal pin interposed therebetween, each aligned with an inner circumferential surface of the housing, and are each bent with respect to a reference axis extending in the longitudinal direction of the housing, so that strip-shaped flat portions face each other,