To provide a blade tool breakage detection device capable of detecting the presence or absence of the breakage of a blade tool accurately without causing a failure.

This blade tool breakage detection device is provided with a sensing means 2 reacting to the change of pressure and a change means 5 producing a pressure different from a constant pressure in a flow passage in the flow passage whose pressure is held at the constant pressure. In this case, the change means 5 changes over to a condition in which a pressure is changed to a different pressure from a condition in which a pressure is held at a constant pressure mechanically by pushing an operation part 6 in by a blade tool 7.