A wavelength conversion device comprising: a light source configured to generate excitation light; a laser medium configured to generate fundamental light from the excitation light; a curved resonator mirror with a curvature radius R configured to form a resonator for the fundamental light in cooperation with a mirror located on a surface of the laser medium opposite to the curved resonator mirror; and a wavelength convertor (140, 240) configured to convert wavelength from the fundamental light into harmonic light (HL, HL1, HL2), wherein the wavelength convertor (140, 240) includes a first end surface (141, 241) inclined by an angle θ from a surface orthogonal to an optical axis of the resonator and a second end surface (142, 242) parallel to the first end surface (141, 241), and characterized in that the angle θ satisfies a relationship represented by Formulas 1 to 5 described below: Spreading Angle of Harmonic Light < θ < θ 1 = 1 2 tan − 1 φ 1 + φ 2 2 L 1 where, L 1: length of the laser medium in an optical axis direction, and φ1 and φ2 are defined by Formula 2: φ 1 = 2 λ 2 π 4 L R − L φ 2 = 1 + 2 L 1 2 π n 0 φ 1 2 4 λ 2 φ 1 where, λ: wavelength of the fundamental light, L: resonator length, π: circular constant, and no is defined by Formula 3: n 0 = n ′ L ′ where n' is defined by Formula 4 and L' is defined by Formula 5: n ′ = n 1 L 1 + n 2 L 2 − L 1 + L 2 − L 1 cos 2 θ + L 1 cos sin − 1 n 1 n 2 sin 2 θ where, n 1: refractive index of the laser medium, n 2: refractive index between the laser medium and the wavelength convertor (140, 240), L 2: distance from the laser medium to the wavelength convertor (140, 240), L ′ = L 2 + L 2 − L 1 cos 2 θ + L 1 cos sin − 1 n 1 n 2 sin 2 θ. a light source configured to generate excitation light; a laser medium configured to generate fundamental light from the excitation light; a curved resonator mirror with a curvature radius R configured to form a resonator for the fundamental light in cooperation with a mirror located on a surface of the laser medium opposite to the curved resonator mirror; and a wavelength convertor (140, 240) configured to convert wavelength from the fundamental light into harmonic light (HL, HL1, HL2), wherein the wavelength convertor (140, 240) includes a first end surface (141, 241) inclined by an angle θ from a surface orthogonal to an optical axis of the resonator and a second end surface (142, 242) parallel to the first end surface (141, 241), and characterized in that the angle θ satisfies a relationship represented by Formulas 1 to 5 described below: Spreading Angle of Harmonic Light < θ < θ 1 = 1 2 tan − 1 φ 1 + φ 2 2 L 1 where, L 1: length of the laser medium in an optical axis direction, and φ1 and φ2 are defined by Formula 2: φ 1 = 2 λ 2 π 4 L R − L φ 2 = 1 + 2 L 1 2 π n 0 φ 1 2 4 λ 2 φ 1 where, λ: wavelength of the fundamental light, L: resonator length, π: circular constant, and no is defined by Formula 3: n 0 = n ′ L ′ where n' is defined by Formula 4 and L' is defined by Formula 5: n ′ = n 1 L 1 + n 2 L 2 − L 1 + L 2 − L 1 cos 2 θ + L 1 cos sin − 1 n 1 n 2 sin 2 θ where, n 1: refractive index of the laser medium, n 2: refractive index between the laser medium and the wavelength convertor (140, 240), L 2: distance from the laser medium to the wavelength convertor (140, 240), L ′ = L 2 + L 2 − L 1 cos 2 θ + L 1 cos sin − 1 n 1 n 2 sin 2 θ. λ: wavelength of the fundamental light, L: resonator length, π: circular constant, n 1: refractive index of the laser medium, n 2: refractive index between the laser medium and the wavelength convertor (140, 240), L 2: distance from the laser medium to the wavelength convertor (140, 240),