A device for ultrasonic peening of metals is intended for strengthening and relaxation treatment of metal surfaces with an ultrasonic oscillation and includes an ultrasonic generator (1) having the optimized power of from 0.2 to 0.5 kW, a piezoelectric transducer with an ultrasonic velocity transformer (6) and a set of readily replaceable heads with striking tools (pins). Various sizes and arrangements of the tools allow for ultrasonic peening of parts of complicated configuration fast and efficiently. In the device, drop-wise cooling and lubrication of striking tools, as well as of treatment area are provided.