PURPOSE: To make it effective for accurate electro-discharge machining performance, by installing a mechanism capable of measuring the tension of an electrode wire directly and accurately, in case of an electrode wire feed system for electro-discharge machining use.

CONSTITUTION: One roller 51 included in an electrode wire feed system is supported by a lever 53 via an elastic body or a spring 52. Likewise, gear-pinions 55 and 56 from a tension displacement spread mechanism spreading the angle displacement of the lever 53. For your information, this wire feed system comprises a pointer 57 and a scale 58 interlocking the pinion 56. With this constitution, wire tension can be directly detected, and when anything unusual happens in the machining electrode wire feed system, inclusive of a secular change, trouble or the like in a pulverulent body type brake, any change in the wire tension can be detected at one so that it is very effective for accurate machining performance.