A harmonics generating device including a supporting substrate; a wavelength conversion layer having a three-dimensional optical waveguide provided with a periodic domain inversion structure therein, a base adhesive layer for adhering a lower face of the wavelength conversion layer to the supporting substrate; an upper-side substrate provided on an upper face side of the wavelength conversion layer; an upper-side adhesive layer for adhering the wavelength conversion layer to the upper-side substrate; an incident face of a fundamental wave, a projection face of higher harmonics, a first side face between the incident face and the projection face; and a second side face opposing the first side face. A first conductive material contacts the first side face, a second conductive material contacts the second side face, and the first and second conductive materials are electrically connected.