We demonstrate the generation of intense terahertz (THz) pulse from laser-wire interaction. Laser pulse with 700mJ pulse energy and 32fs pulse duration is focused on a metal wire. Electrons emit from the wire and create a time-varying radial electric field which forms a miniaturized gyrotron-like undulator. Over 3 mJ single-cycle THz pulse is generated from the undulator. By using a tip at the end of the wire, the THz electric field is enhanced to 90GV/m. The high energy single-cycle THz pulse and the enhanced strong electric field provide a powerful tool for studying THz matter manipulation and THz nonlinear effects.