A submillimeter wave of 0.34-mm wavelength with peak power of ∼10-3watt has been generated in ZnTe by beating the R1and R2lines of aQ-switched ruby laser. As the detectorn-InSb cooled to 1.7°K was used. The dependence of the beat power upon the angle between incident electric fields and the crystallographic axis was in accordance with the43msymmetry. The observed beat power was smaller, by three orders of magnitude, than the calculated one based on the assumption of collinear plane waves. A theory including the effect of input beam divergence inside the crystal gives a beat power fairly close to the measured value. Some results of auxiliary experiments supporting our viewpoint are also given.