We present a new automatic code (ARES) for the determination of equivalent widths of absorption lines present in stellar spectra. We also describe its use for the determination of fundamental spectroscopic stellar parameters. The code is written in C++ based on the standard method of determining EWs, and is available for the community. We test the code using both simulated and real spectra with different levels of resolution and noise comparing its measurements to the manual ones obtained in the standard way. The results are very satisfactory. The code will be used for the accurate determination of spectroscopic stellar parameters and chemical composition for a sample of bright solar-type stars suitable for asteroseismology.