High power terahertz (THz) radiation was generated from photocomductive diamond switch array for the first time. This device consisted of more than 2000 photoconductive gaps and a binary mask for spatial modulation of pumping laser. Due to the high breakdown threshold of diamond and the over-coated gap structure for preventing surface flashover, high electric field strength (2x10~6V/cm) can be applied on each gap with DC mode. A 10nJ, 1.5ps FWHM free propagating electro-magnetic pulse was observed from 10mm~2 effective emission area at E=10~5V/cm. This radiation was focused on to 1.4mm spot with F/2 optics. As there was no severe saturation observed in photoconductive phenomena in CVD diamond up to 10~6V/cm. the focusing intensity can be increased to GW/cm~2 level by increasing the applied electric field and the switching area.
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