Disclosed is a terahertz wave generator which includes a first light source outputting a first light having a first frequency; a second light source outputting a second light having a second frequency different from the first frequency; a second harmonic generation unit performing second harmonic conversion on the first and second lights to generate a third light and a fourth light; and a photomixer converting a mixing light of the third and fourth lights into a terahertz wave alternating signal and outputting a terahertz wave.