Abstrak— Therapy tool is a tool used to stimulate the body parts that want one example is Electrical Stimulation, one example of electrical stimulator tool that is FES (Functional Electrical Stimulation). FES is a method that applies a low level of electric shock to the body to restore and enhance the day-to-day activities of patients who have spinal injuries, one of which is in the Lower Limb section. On this occasion the author wanted to create a "Functional Electrical Stimulation build for Lower Limb muscle Rehabilitation". In this electrostimulator use surface electrode highly recommended, besides being non-invasive electrode, this electrode also provides comfort and easy to use. (Azman, DKK: 2012} This tool uses Biphasic Simetric Square Wave pulse form. The study used a pre-experimental type with One Group post test design research design. Measurements are done 5 times the digital oscilloscope. At the oscilloscope is the frequency of the smallest error value 0.08% and the largest error of 1% and the voltage measurements on the oscilloscope have the smallest error value and the largest error of 0%.