We demonstrated broadband terahertz (THz) wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam. We constructed a dual-wavelength optical parametric oscillator with two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. The collinear pump and signal waves were irradiated into a lithium niobate crystal. The pump and the signal waves were reflected at the crystal surface. Because the pump and the signal waves have a finite beam diameter, when the reflected signal wave and unreflected pump wave were irradiated at the correct angle, the noncollinear phase-matching condition was satisfied. By changing the incident angle to the crystal, broadband THz-wave generation with a range of over 0.2-7.2 THz was achieved.