To prevent incapability of detecting breakage of a tool owing to wear of a wire due to contact of a wire to a tool, in a wire contact system tool breakage detecting device.

When a tool 23 free from breakage enters a detecting region F, the tool 23 interrupts a jet A of compressed air, and the jet A is brought into a state that the jet is not collided with a working fluid support part 15 of the plunger 14. The plunger 14 is moved to the injection nozzle 5 side through the spring force of a spring member 18 to cause a microswitch 8 to effect OFF operation. When the tool 23 having breakage enters a detecting region, since the jet A of compressed air is not interrupted by the tool 23, the jet A maintains a state to be collided with the operation fluid receiving part 15 and the microswitch 8 is maintained in an ON-operation state. Thus, the breakage state of the tool is detected by an ON and OFF signal of the microswitch 8.