PURPOSE: To enable detection of over-heating of the cylinder and improve the safety characteristic by a method wherein a plurality of cylinders are arranged within one cylinder cover and a temperature fuse fixing plate having the temperature fuse inserted and held at a box-like part is fixed to each of the cylinders.
CONSTITUTION: Since a cylinder cover 25 is integrally formed with a right cylinder 21 and a left cylinder 21, a spacing in which a cylinder expanding part 39 is exposed and a temperature fuse 43 is placed shows a high temperature. However, a fuse 43 is positioned below the cylinder cover 25 and its atmosphere is kept at a relatively low temperature and at the same time a melting cut temperature is set at a sufficiently high temperature, so that the fuse 43 is not operated under a normal operating state. However, if a heater 22 is continuously and electrically energized due to an abnormal state of a thermistor for sensing the cylinder temperature or a control device and the cylinder 21 shows an abnormal over-heating state, its temperature is transmitted to the fuse 43 by the temperature fuse fixing plate 40, the fuse 43 is operated to stop the electrical energization for the heater 22. At this time, a temperature sensing part of the fuse 43 is substantially covered by a box-like temperature fuse holding part 41, so that an atmospheric temperature at the temperature sensing part is rapidly increased and the over-heating at the cylinder 21 is positively detected.