A diaphragm type actuator with a breakage condition detecting function which comprises a diaphragm member partitioning a casing into a first chamber filled with a high pressure and a second chamber exposed to air, and a breakage detecting switch supported by a displaceable partitioning member, such as, bellows, provided on the inner wall of the first chamber so as to define a third chamber filled with a high pressure, whereby if there occurs breakage in the diaphragm, the breakage detecting switch mounted on the bellows moves towards the diaphragm member to become in contact with an actuating rod supported by the diaphragm member to detect the breakage in the diaphragm member.
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