The generation of coherent optical phonons in an antimony film has been directly observed by the femtosecond electron diffraction method. The sample has been excited by a femtosecond laser pulse (lambda = 800 nm) and probed with a pulsed photoelectron beam. Oscillations of the intensity corresponding to vibration frequencies of optical phonons excited by the laser have been observed in the obtained diffraction patterns: totally symmetric (A (1g)) and twofold degenerate (E (2g)) phonon modes of antimony and their combinations.