PURPOSE: To obtain the reliable, inexpensive and also small display means of a heating circuit by combinating a thermosensitive mechanical element with an operation element and executing the motion of the operation element to an operation position during shift to a second specified state.

CONSTITUTION: A spring 22 is in the first state, that is, the compression state in the stop position of the display device. When the display device and a surgical device are heated, the spring 22 is powerfully extended but, in the meantime, a safety spring 18 keeps its original measure as far as the display device is not heated to have excessively high temp. The extended spring 22 moves an shaft 13 to a right side and it is fevorably power ful to compress a reset spring 22. The free end 33 of a ratchet 32 is interlocked with the steeply inclined side of a nearest tooth 5 so as to rotate a ratchet wheel 4 clockwise. When the ratchet 32 reaches the operation position(the spring 22 is positioned at the second specified position), the ratchet wheel 4 is rotated for the portion of one tooth, that is, till the second ratchet 38 passes the tip of the pressed tooth so as to be fall.