A wavelength conversion apparatus in which output direction of a wavelength-converted laser beam, having a wavelength converted by a nonlinear optical crystal and emitted through an output-window, can be brought close to the direction of optical axis of the laser beam passing through the nonlinear optical crystal. In addition, axial deviation of the wavelength-converted laser beam converted by the nonlinear optical crystal and emitted through an output-window, can be reduced when the position of the nonlinear optical crystal is moved. The output facet of the nonlinear optical crystal is inclined at Brewster's angle with respect to the wavelength-converted laser beam. An output-window of a case containing the nonlinear optical crystal has a prism form in which the distance between a laser beam input facet and a laser beam output facet of the output-window is reduced along a direction in which the wavelength-converted laser beam, emitted from the nonlinear optical crystal, inclines.